it depends on
a) how good your new comp is
b) how much time you're willing to put into it
c) whether u like old-school cookie cutter rts or sth a little more revolutionary

a) You need a Core 2 Duo E6600 or better to run supcom. System requirements on C&C3 aren't nearly as high. graphics-wise.
b) Supcom requires a fair bit of time to master. C&C3 is a standard rts
c) Supcom is fairly revolutionary what with the zooming out, the streamlined base-building, the better resource system, the waypoint system that actually work, and the massive scale. C&C3 follows the standard rts fomula to the very letter.

Magic in oblivion is BROKEN. essentially, being a mage is too easy and being anything else is tough unless u get the combat system which i never did after a hundred hours of playing. 

Paralysis is so cheap its not even funny. its even more atrocious how your blade skill goes up even when ur hacking an inanimate object.

i personally like invisibility. helps me avoid all those damned demons without having to bother with actually fighting them *gasp*. gets boring fighting them over and over again. The level up with u so u dnt ever get the satisfaction of pwning them hard then moving onto sth more difficult.

a nice cheap combo i find is to get that rechargeable soul gem, put an absolutely crazy enchantment, i.e. 70 fire damage, on my demonic looking sword (the best one) with a soul steal enchanment. that way my swords (i keep an ice, fire and a poison sword all with the same crazy enchantment...just specialized) are constantly charged. i am a high-elf archmage with 100 sword skill and a full set of enchanted demonic armor... i got bored of oblivion pretty fast. havent played it in ages which is why i forget the details.

oh and lets not forget feather. i LOVE that spell. its cheap and triples the amount of stuff i can carry with multiple casts. kinda defeats the point of being a strength based character. a mage does everything so much better.

Company of Heroes definitely. Pick up supreme commander too while u're at it. They complement each other nicely. Coh is all abt micro and supcom is all abt macro. u'll need a rly good comp and a decent internet connection for supcom tho. Nonetheless, both are "next-gen" rts.

You might as well get {insert generic RTS such as AoE} rather than C&C 3. it'll be cheaper and its essentially the same thing.

veyr simple. SUPREME COMMANDER IS NOT A SINGLEPLAYER GAME. it will bore you to tears. you will cry from how bad the ai is. you HAVE to play online. oh and by ppl saying C&C3 being more traditional, picture ure run-of-the-mill rts which has no innovation, a good storyline and nice graphics, but nohing original. CoH is a mcro-e's dream. not my thing but its a great game.

trust me you will never notice supcom's graphics which i daresay are only slightly better than warcraft except for the explosions. most of the time u will be zoomed out (love that feature).

 Its NOT possible to have 7 AI and a 1000 unit cap with a smooth framerate. not this side of 2007. 

All boils down to whether you like fps or rpgs more. stalker is primarily an fps with rpg elements. oblivion is rpg at its greatest

oblivion will get you hooked quickly, u'll stay on that high for a couple days of continuous playing, then it lets you down badly when you realize how repetitive it is. oh and that the mage class is broken (*cough* paralysis *cough* and *cough* feather(for carrying all your loot) *cough*) while good luck getting anywhere as a melee or archer guy. I confess. being an archer is probably one of the best parts of oblivion. it's one of the few things that have actually got my pulse racing (concerning gaming).

STALKER i have not played but i REALLY want to.