ATT has most market share by far..
as for the phones:
Sony ericsson X10 is coming out, and its said to be better than the iphone 3gs
iphone 3gs by apple currently the best phone available for a mainstream audience
Sony ericsson cypershot C905a has a 13.1 mega pixel camera, and a touch screen with a walkman pre installed among other features
Best black berries are on ATT
the new samsung impression just came out to ATT
etc..