You should go with the PS3. I bought an Xbox 360 because it was cheaper at the time, but I've got to spend 50 bucks a year only to have my own internet on the motherfucker. Maybe it has a few games more than the PS3 but that's the only plus side. If I were you I would go with the PS3

If you're going to get one eventually, and that eventually ends up being a few years, don't get a PS3. Just get the PS4 instead.

But other than that little piece, I know nothing about the two systems. Sorry.
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I was in the same situation myself. I did not care about having the Blu-ray player or better graphics. I went with the PS3 because my best friends had it, and at that moment we all lived in separate states across the east coast (NY, NC, and FL). The whole console war is very stupid in my opinion and all consoles should be valued for their gameplay experience; however, if you only want to stick with one console, you have to know that you win in some aspects, and you lose in others.

With my friends I've played Dark Souls, Modern Warfare 3, Warhawk, Demon's Souls, Marvel Vs Capcom 3, Uncharted 2, etc.

Hello kind sir, first I want to state that I currently own a PS3 and an Xbox 360 (and a high end gaming PC). Now that that is over with, here we go.
Generally speaking it depends on what you want out of the console.
The Xbox 360 does have halo, but not the halo that you and I fell in love with. You know what I mean. Going over to a friends house and playing four player split screen infection on some ridiculously fun map. Yeah, that Halo died years ago. Now that I have that rant out of the way lets run through some pros and cons for each console.
Xbox 360
Pros:
halo and gears of war, DLC is released early, Excellent Dashboard,
xbox live parties can be used in every game
cons:
$50 a year for xbox live, RROD (depending on which model you buy), Controllers use AA batteries.
Before I want to run through the pros and cons of the PS3 I want to mention that while the PS3 does not have halo, but it does have Metal Gear Solid 4. Which in my opinion surpasses. (had to get that off my chest)
PS3
Pros
Free online play, Metal gear solid 4, Blu-ray player, integrated wireless adapter, PS3 controllers are rechargeable via mini USB cable. (don't use AA batteries), PS3 uses Blu-ray as its media which can hold up to 25gb (Xbox's Dual layered DVDs only can hold 8.7gb. Often forcing games to have multiple discs), Integrated Bluetooth, internet browser
Cons:
Delayed DLC, PSN has been hacked, no private chat parties

So here we are at the end of my comparison. I had the xbox for 3 years. It was good fun, but now I gave it to my brother. I rarely play it compared to the amount of time I spend on my PS3. So when it comes down to it, if all you want is halo...
You should still get a PS3.
Message me when you're on PSN.

Hope I helped.