which is better?
I hope the SEARCH button on top of page is still working.
If not, try a search for "3500 different 3520" or the other way around.
BTW, I hope 3520 is "better".
You could ask what's the difference between stupidity and intelligence, and the answer would be '1 post'
3520a should be better because it is the latest but the only drawback is the 3500a has been out for a while and has therfore had more time to have the firmware tweeked..But if i were buying one now go for the 3520a