Portable gaming which can fit in your pocket or just barely doesn't fit... but they can either be bucket loads or fun or something which you regret having set your eyes on. Either way, both of these current gen handheld entertainment systems have proven their worth and is great in their own respects. These systems are the Nintendo DS (Duel Screen) and the Sony PSP (PlayStation Portable). Each have its downsides and upsides, or maybe it isn't.
Upon release DS: The DS was chunky and may of had problems with screen brightness and was only made to play games, nothing more but it can not play Gameboy games, can't forget about those grey odd chunkish cartridges (not grey depending on some games). The system doesn't require constant updating in case some game required more function as whatever is on the system is what you get without a question of any possible optional goodies. Isn't very powerful, but hey, they have the best reputation when it comes to battery life!
Upon Release PSP: Kinda wide, but no that chunky as the original DS, can play music, movies, surf the net, play games, view pictures, connect to the computer for file transfers and more! Built as a device close enough to a PC, but in a really portable size!

--Rants--
DS: When I saw it first come out, I saw very little of it and didn't think much of the touch screen and called it something to avoid. Not because it is a bad system, but because of the possibility of personal enjoyment. Nintendo does really well in terms of advertising as rather than advertise about what you can do with it, they let you try out each functionality as you come across it rather than telling at there's a mic, slot to put in a Gameboy Advance games, use the touch screen to interact in the game, having the possibility of one unless screen during a game and shoddy music quality.
PSP: First thing I did when I got the PSP, I was only interested in testing out all those neat features I was advertised about and then check out the game collection, big problem being that there weren't a lot of games which caught my attention (oops!). Then resorted mucking around with the PSP a bit only to of realised that the amount of hype surrounding the system was a false pretence. I know there are many PSP fans out there which absolutely call it a godly device, better than the DS, but hell, I couldn't really enjoy myself with that system with the exception of watching video clips on that damn thing. Other than that, it is just collecting dust in my drawer as we speak, even contemplating letting someone borrow it for a few months since I haven't touched it. The controls were shoddy to bits, after playing for a good long while, my neck was hurting for hours, it was very awkward in my pocket and bag, discs were annoying to carry around, speakers weren't loud enough, infrared was unless and was dead weight. In plain short, the surrounding advertising and mass hype, was greatly disappointing.

--Praise--
DS: After playing the DS for hours, I kept checking both the top screen and bottom, reducing neck cramps after play, cartridges were small so it reduced loading times, but it very fragile in return, but at least it is very light! The touchscreen is hella easy to understand, even giving it to someone who hasn't touched a DS in their entire life, will get the concept straight away (tried and tested), the device doesn't have real weak spots unless you really have a go at the touchscreen and buttons down to understandable logic. The DS is just like the SNES (Super Nintendo Entertainment System) controller with the exception of two screens, bugger loads of power, much more smarter (for all those electronic geeks, don't flood me about the oxymoron there) and you can carry it anywhere and play it without looking like an idiot!
PSP: Play music, watch movies, watch TV episodes, watch whatever you want, play games, look at photos, set your own wallpaper (on the PSP), browse the internet, play WiFi or Ad-hoc with someone else in the room, wide mini screen, same buttons as the Playstion controllers was the exception of an R2 and L2, with other buttons to set whatever on that thing.

--New Spawns--
DS: Fits in your pockets better, can make the screen a lot brighter, lighter in weight, had lots of plastic surgery, face lift, some off features placed elsewhere, comes in many more colours than one the original realise (six colours now I believe, and custom tats to the special ones), no unless bits (as always) and two and visible lights, one for charging (off if finished and on if charging) and the other to indicate battery life (red for bad, green for good).
PSP2000?!?: 7 years too late, would anyone still care about that year? Anyway, it is lighter, thinner, but it doesn't mean that the screen will be smaller, no infrared, smaller battery with same life expectancy, button issue fixed, still uses UMD, just like the PSP but less. It is like the system went anorexic! Does the same damn thing, is the same system, feel like the non-rexic version, does one extra thing, still tries to slap abusers across the face.

--Judgement--
DS: Hell, the games are great, I don't need to constantly update my system to do new things, I'm always playing with it , or as much as possible, OMG, it is actually fun, hardly crashes (expect if you try to cheat too much), good homebrewers around, Mario is still around and hell, I haven't ever suffered a cramp at all when I'm always playing the system! If you own one and hardly use it, try playing some casual games or some game that allows constant saving of data. Chances are, you'll come back to it a lot more
PSP: Sony just has scandal after scandal after scandal, just not a good launching platform for promoting the PSP and does anyone even bother with the UMD movies on the system? I mean, if you at least had a cheapskate side within you, you'd figure out a money saving way to avoid the UMD movies and tried to experiment a bit. Right now, I've not no real use for it and doubt I'll be using it any time soon. First there weren't a lot of good and interesting titles to my liking and don't tell me about GTA about being on it as it ain't my type even though it is a FPS, I prefer FPS on my computer than something which isn't that powerful. If something isn't deemed "fun" would you touch it?

--Future--
Before Gameboy Advance, you have a very "very" small market of Neo-Geo Pocket fans out there playing and then it was reduced to just one, which, of course, is the GBA (I know about the N-Gage but has been seen to be an absolute joke). Possibilities on the horizon beyond this current Gen. The new Nintendo device will have a Wii like interaction or six-axis, possible names, 'Nintendo Shift', 'Nintendo Move', 'Nintendo Tilt' or 'Nintendo Shake' (aka Ninten-quake).
Nice try to the PSP and a system which I hardly enjoy due to so many un-interesting titles which I don't really fancy myself playing, though, I've been meaning to get my hands on Locoroco and some weird music game, I'm up for guessing a foldable screen to fit in the pocket a lot better, like splitting the widescreen in half. One side holding the UMD and the other side for the battery. Along with the fold, the D-pad and analogue will on one side with the other having the standard four buttons. With the folding feature, there is a click in so it seem like there really isn't a fold in the middle of the system, though, the neck problems will persist. Dibs on 'Playstation Fold!'

I'm not just going to end it there, I'm guessing a possible three more players which many enter into the handheld war!

Sega may choose to re-enter the race, either to compete or assist. There has been a question mark over their head in regards to the reserving rights to Dreamcast 2. My bet is on a handheld. Their Game Gear wasn't an absolute flop, just pulled out at the wrong possible time, that's all.
Apple may also enter the race with their iPod being able to play games on it. With many iPod users chucking on their solitaire or some other homebrew program as a bit of time killer of boredom. This must be something which Apple must be considering since they have realised the Macbook Air, which is hyper thin, even thin enough to compete against the DS or PSP in the thinnest model awards.
Discounting mobile phones as a proper handheld entertainment device as they are on a league on their own, but there's a possibility of a return by Nokia with round two of their N-Gage. I was suppose to go with Microsoft, but with the failure of their Zune, I doubt they will attempt to fight that market unless they choose to tag with Nokia by supporting them with games, which may actually boost both their egos.

Keep the good titles rolling to build interest otherwise it would of been cheaper to of dumped the cash into a country which doesn't even need it, like Monaco.
If a handheld isn't made to be enjoyed, where's the personal enjoyment in that?