I've had great results with my autofocus lenses, but then again, I only have two: the 28-105 and the 24-50. Both of them focus extremely fast, but they don't have the weight and heft that the manual focus lenses have. I can't really tell a difference in quality between the two...I would be hard-pressed to tell you whether or not a negative came from the newer 24-50 lens set at 50mm on my F100, or my old 50mm f1.4 that stays on my '68 vintage F. I will say that the only lens I've had issues with (and needed repaired) was an old 55 Micro...but I'm also reasonably careful with my equipment, so it tends to last awhile. As far as overall speed is concerned, even a lightning-quick autofocus lens won't work as fast as a hyperfocal setting...and if I'm working with narrow lenses that don't really support a hyperfocal technique, I usually have all the time I need for focusing. Overall, though: no problems with the autofocus lenses...they work well for me.