I was wondering if i should get this or Fat princess? 
I cannot make up my mind which game to get, I can get both but I don't want spend a lot of money

i say keep this one's money for Battlefield Bad Company 2

I put 20 hours into it and really enjoyed, havent got fat princess so I cant comment on that

Both are worthy picks.
 
If you are more of a competitive gamer, I would get Battlefield 1943.  It's a very solid FPS game with expansive maps and well balanced classes.  You can really approach the combat any way you want, whether you like sniping, going run-n-gun, or being like a spy and sneaking around (my favorite thing to do is to parachute out of a plane and land on the roof near the flag; I take the enemy's flag location and shoot anyone nearby from above without them even knowing my location).  My only issue with the game is that there are only 3 maps (4 if you include the airplane-only map Corral Sea) and DICE has no current plans to release DLC.
 
if you want a more laid back experience, get Fat Princess.  There are a of ways you can help in the battle, whether it is to be a warrior and take the enemy head on, or be a worker and upgrade weapons (hats) and help defend the base.  It's hard to find a game with a team that is working together, since the game is so hectic.  Also, there is no auto- team balancing, so people all switch to a winning team once a round is over.  That is what kills the competitive aspect of the game, but it's still just fun to run around a cause mayhem.

" i say keep this one's money for Battlefield Bad Company 2 "

DICE have done a great job here. Excellent ranking system with in-game goals (stamps and postcards) that reward the returning player. 
 
When things kick off, with tanks rolling in, planes diving and troops exchanging fire, it feels truly epic. Took me +20 games to really appreciate what a rewarding and nuanced game it is. Can't speak to Fat Princess but 1943 gets a big thumbsup

It's $10 now so I figure it's not a bad way to pass the time 'til BC2. I've never played a Battlefield game before, or even really been into online shooters, but BC2 has me seriously hyped and I really enjoyed the 1943 demo.

Get 1943 over fat princess. If you can afford 1943 AND BC2 by all means buy them both. If not save your money for BC2.

get battlefield  1943