American made makes no difference anymore in terms of the workmanship. taiwan used to be a bit dodgy in terms of the quality of welds and metals but they are as good if not better than most european and american companies now. if anything american just means it will be more expensive, as american labour is far more expensive than taiwanese.
having said that S&M's are sweet, i used to ride one when i had trails and it was really nice and stable. (just wanted to make the point that you shouldnt buy one just because its american)
once i moved house i got a sputnic satelite, then a WTP elektro and i now have a WTP a2b. i cracked the elektro and WTP gave me the a2b for free.
Thats a good enough reason for me to recomend them, as i know a number of people who have had problems claiming warranties, particuarly for s&m stuff.
to be honest all new frames have pretty much the same geometry, ride really nicely and weigh bugger alll. so i'd go for whichever you like the look of and can get cheaply.