I have to say the best of the tele zooms I used was either the 100-300L - which was noticably sharper than the standard 100-300, or the 80-200/4 - 2 touch lens..and funnily enough I always found the 70-210 to be much sharper than the 75-200..and I owned a couple of versions of each lens...

And yes - the cheap platic 35-70 that everyone dismisses is a surprisingly good lens - I used to use one as a macro lens when I was repairing cameras to photograph the insides of cameras