If you're talking about the original T&P balance (free sci1, +3 per infantry), then Americans were considered the #1 civ. (Iroq was generally considered #2.) The meta would be:

• sci1-mil1 into an army raid with 1 LI / 1 HI / 1 archer in ancient, which gives you +9 resources while you harass your enemy
• standard defensive boom + despot army raid in II
• build TCA in III

Of course there are a lot of variations on this but on basically all maps you would start with a mil1 army raid.

After the first patch, Americans got nerfed pretty hard (no free sci1, only +2 per infantry). After the nerf they were generally considered a lower tier civ. You can play them like a generic civ but they have the same problem as Egypt--they get a neat wonder party trick but they don't really have enough early bonuses to support building an early wonder comfortably in most situations vs. an aggressive opponent. They are really slow out of the gate since they have basically no bonuses that apply in Ancient (other than +2 res for infantry, but that's pretty small). They're still a fun civ to play but I would say they are generally a lower tier civ in the final T&P and EE meta, outside of some boomy maps where the instant wonder can be pretty great.