Help me pick games...

Get neither.
Why?
Neither of them are on sale.

Get Payday 2 ,It won't go on sale until the Winter sale.

Payday 2 if you have friends to play with.
Left 4 Dead 2 if you also have friends to play with.

:D

Payday 2 I HATED the first Payday but after playing the beta of Payday 2 I ended up getting the second one the first day and its worth it if you have other friends that own it as well.

L4D2 is really fun to play and like TotallyNotBarto said about the friends. Payday 2 seems interesting to play though

PayDay 2. :)

Payday 2 because L4D2 goes on sale all the time, so odds are you'll be able to pick it up cheaper later. That said, I think L4D2 is arguably the better game.

Haven't played either, but I'll say payday 2 .simply because I'm tired of zombies. And yes, this despite the fact that l4d2 appeared at the start of the zombie craze.

Payday 2 because you can get L4D2 really cheaply during sales

Payday 2, you will have to play with friends or a good team to get the full potential out of it, I enjoy it a lot though so I can only reccomend it!

Get Payday first. I doubt it's gonna go on sale any time soon and Valve games should get at least 75% off now each sale since it's been a while since their last game.

Payday 2 to play with friends (I have Payday: The Heist, so I guess Payday 2 should be almost the same gameplay). As for L4D2 I don't know.