For those who doesnt know what CC is its Castle Crashers so far its only been released on Xbox but is coming to PSN the 31st in NA (dunno european release yet) 
 
So my question is what should i get ? i dont plan on buying more than 1 at the moment so im dragging toward CC because of multiplayer but maybe shank is more fun ?

1. Try demos
2. Do you have friends you can play Castle Crashers locally with, or PSN friends willing to buy it?

Both of them feel like glorified Flash games in my opinion.
 
I wasn't impressed with the PSN demo of Shank but you can download and try it on your own. 
 
Castle Crashers is pretty good, but every time I play it at my friends house I crave proper beat-em-ups done by Capcom.

" Both of them feel like glorified Flash games in my opinion."

Honestly...I'd say wait for Castle Crashers.  I agree with others, they really are both glorified flash games...but of the two I think Castle Crashers is better.  Shank was good, but short...and I don't see as much re-playability with it, though I didn't try the local co-op mode yet as I just got the game today, but after I try that my opinion might change.  Castle Crasher's on the other hand I spent much more time on.  A big difference is you get different characters that you can keep playing with to rank up their level/stats, and tons of other unlockable characters that you earn by beating the game with another character.  And in many cases, after you beat the game with one character and unlock a new character, you'll unlock another character after beating it with that character.  So...tons of re-playability there...if you like the game at least.  
 
Castle Crashers also has online multiplayer which greatly helps with the re-playability factor if you have friends that are willing to buy the game and play it with you.  It also has local multiplayer for when your friends come over to your house.   Tons of unlockable characters, weapons, and animals to find in Castle Crashers, where Shank really doesn't seem to have many unlocks, though it does have a few costumes to unlock. 
 
So, the obvious choice for me would be Castle Crashers...but I suggest you wait until the demo is out, and try both of the demo's.  Only you can decide which one you'll enjoy more.  If you're not a big multiplayer fan, Shank may be more for you.  I didn't really find Castle Crashers fun by myself, so I wouldn't suggest it unless you have friends to play with.  And Shank may not even be worth your time for $15 unless you really loved the demo and think you'll enjoy the game.   I'd actually probably recommend saving your $15 before buying Shank.  But if you can play Castle Crashers on multiplayer, go for it.