TBH, in the GAME both of them are squad players at best IMO assuming you are playing as Arsenal. I've had much success playing Walcott and van Persie as my two forwards. But I would probably go with Bendtner in the game, since he is a little bit well-rounded and much taller. Chamakh is awesome too if you play him correctly.
How would you play both of them? Would they both be target men? With Bendtner attacking and with balls to head and Chamakh support and balls to feet?
I never seem to get the best out of either of them, although bendtner does dominate smaller defenses in the lower leagues with I play in cups...