Judging by the odds from the bookmakers, it will be an approximately equal match with a slight advantage for Arsenal:
2,19 - 3,60 - 3,30
but in my opinion Arsenal is now on the rise and is more likely to win (accordingly, a bet on it is profitable). A safer bet is BTTS with odds of 1.67, both teams are good in attack, so BTTS looks adequate too.
Arsenal have a really tough work to do ahead of them. They may be at a nice place in the table now but their latest form is not very acceptable for them. They lost thrice in their last five games in the EPL. They still have improved their morale by the solid 3-0 win vs Southampton. But West Ham is a much more serious opponent for them regarding West Ham's a little better condition than them. I guess I won't bet on this game.
These defeats were from strong clubs and came after a great unbeaten run from Arsenal. If Arsenal beat everyone, then now they would be the leader of the EPL (logical isn't it?). Losses sometimes happen to everyone, I judge by the shape of Arsenal, I think they are on the rise.