Welbeck has plenty of things he needs to improve upon, and I certainly like and appreciate that Giroud works hard for the team. As Flobobski says, it is more down to the different types of football they represent for me. I also don't like that we attempt to play in the exact same way regardless of whether it is Giroud, Alexis or Welbeck at point. Doesn't seem very smart to me.
The only time, that I can clearly remember at least, when we actually looked to play differently was the game when Alexis was at point and flanked by Campbell and Walcott. The wingers kept width quite well, and when Alexis dropped deep to receive the ball they looked to exploit the space that opened up with runs in behind. I much prefer that sort of football, and i think we looked fluent, played an attractive brand of football, and it was effective. That sort of football is just impossible to play with Giroud. It just isn't his game, and his presence doesn't allow for it. In theory, we SHOULD be able to play like that with Welbeck, AND he'd also represent presence up front, the ability to beat a man on his own, runs in behind from him as well, and also an aerial threat on crosses. I am the first to admit that Welbeck is far from there yet, but I am also the first to acknowledge that Welbeck really hasn't played very much as an out and out striker in his career. I want to see him develop his game in that direction, and it sure isn't going to happen if Wenger persists with playing him wide. Ideally, I'd have him ride the pine mostly when Giroud plays, and look to play Welbeck every 3 or so games as a proper striker. If he wants more games, then he needs to improve to the point where he overtakes Giroud on merit. On current form for both players, then Giroud is clearly the better player, and we'd do well to rotate him to keep him fresh, thus looking to prolong this purple patch.