As for which is cheaper, the 160GB PS3 is $250, the 4GB Xbox 360S $200, and the 250GB Xbox 360 is $300. You'll probably want a HDD for Skyrim DLC, so either the 160GB PS3 or 250GB 360 would be your best bet.
There's also the 320GB PS3 for $300, as well as bundle deals like Infamous 2+PS3 320GB for $300 and on November 1st the Uncharted 3+PS3 320GB releases for $300.
There's 360 bundle deals as well, but as far as I can tell (at least for newly released titles) it's about $100 more expensive. Like MW3+A MW3 themed 360 320GB is $400. Same goes for Gears of War 3+GoW3 themed 360 320GB.
There's also, as others have said, exclusives to take into consideration.
PS3 also doesn't take a monthly fee for online play, but the 360 is something like $20-$30 every 3 months but I'm sure it must offer some sort of better online grouping and communication or something along those lines.
They both offer services like Netflix and Hulu, and both have online marketplaces where you can buy games and such.
If you're into the whole "avatar creation", the PS3's avatars on what is called 'Playstation Home' have a more realistic look to them and you can also walk around in different areas to socialize with others and what not, as well as being able to have a virtual home for your avatar (such as the apartment you start with, as well as numerous places you can purchase) where you can decorate or just hang out or whatever. It's really just gimmicky stuff in my opinion, but apparently there are some who like it. The 360's avatars have a more cartoony look to them, but from what I have seen, there's also a lot more options available initially for free when picking out your clothes.
DLC for Skyrim also comes out 30 days earlier on the 360, if that matters to you. As for how it looks and runs, it SHOULD and most likely will (if they've done a proper job) be the same on both consoles.