Tests
Emulators are bad because of the hardware involved. As you know PCs run on specific hardware that transfer well. They evolved as business machines and will stay that way. When graphics are emulated they need the EXACT hardware. This does not transfer well with dreamcast being one example. The Dreamcast runs its hardware with A 12X CDROM. This alone fails to create the most fluid graphics no matter how fast your computer is. The RPM rotates too fast. This creates uneeded bumps in framerate and glitchy hardware effects evident in games like aerowings 2. Harddrives move the gdrom too fast, not to mention the OS is running the graphics all together. Being that said, the O/S is the second mistake. Emulators dont transfer 3d polys well and cant mimic processors. Thats why you see glitches in 3d games on psone, dc, SNES emulators like no shadows etc. They are simply different Gpu graphix manufacturers. The OS simply cant mimic the processor. Win CE on the Dreamcast works the same way as does the sega O/S to an nes snes bleemcast emulator. Bleemcast actually being better because it runs from a CD. From what ive heard Consoles can, PCs cant (from my experience the epsxe Psone emu scratched up both of my 80 dollar ff7 games with possibly too fast hardware being the culprit). Quake I being the only sucessfully emulated game because it was built on the hardware by the publisher for free, so it was kind of cheating:) Like how 360 excels in texture and ps3 in physics/memory the dreamcast excels in hardware (and much more efficience in loading software from the cd than pcs) all together being at the right place in the right time.
Reccomendations
As for consoles, as mentioned, I managed to ruin a 60 dollar psone game, ffx7 because of it, not to name names, but psexe scratches the cds. So I cant even trust emulators unless transfered to the harddrive. Xbox is a different story. Not only can it run mugen, have usb controllers that are comfortable, but it can run emulators on PC/Linux fluidly! If you install linux, ubuntu or whatever, play native video card games like quake 3 or better yet the customized twisted metal 2 on it or a ps2/ps3 windows xp O/S then all that effort to installing it will def. be worth it (note ps2 needs a seagate harddrive of course). Games like tm2 were downgraded ports made for this stuff because they use no video card support and are made to play great on low-grade machines. Doom, quake and open source games are also a valid exception. All in all emulators will always be good for video recording, or quick gameplay try outs ala why the PSP was really made, for DOSbox (an emulator which emulates old shareware games on xp/linux) not Dreamcast emulators. So basically consoles like PSP are the most superior emulating console to date also being widely compatible with open source. Dreamcast and xbox are reccomended for old school gaming while PC is superior in every way but not gaurenteed:P. Not reccomended for avid gamers who want to play through a game fluidly and safely. If you are new to this field, Check out DCemulation or emulationzone.com to get started. Start with popular 16 bit emulators such as kgen or zsnes. 32-bit 64 genre tend to run fast as well. The faster the console the slower the emulation and more unique the hardware, sixth generation consoles are not reccomended, unless you have state-of-the art hardware and like to avoid glitches.