I generally avoid shooting with the sun in my frame, but a couple of times lately I have done it and had big problems. Thing is, both times were with non-USM lenses. One time was with the 50/1.8 and the AF kinda locked up. I had to switch it to MF and back to AF to get the AF to work at all (that may need a repair, happened once in the dark too). The other time was with a Tamron 17-50. In both cases I was in a hurry and didn't get to try he same thing with a USM lens.
Are USM lenses going to do a better job in this situation, or is the camera's AF system to blame?