I've owned both and used both fairly extensively. Currently I have the 20-70, but I think the 30-60WA is the overall winner because the field of view is just so much wider/better. I rarely go above 45 or 50x on either, but wanted to try the 20-70 out for low light conditions. I think at 20x it is a fair bit brighter at minimum magnification; however, the 20-70 is just so much more difficult for me to locate what I'm wanting to look at vs the wide angel eyepiece (I do have the angled model, which makes things harder). I can't be quoted on this, because I haven't done a direct side-by-side comparison, but I would say the 20-70 eyepiece has a tiny bit better center resolution and is clear way out toward the edge too, whereas the 30-60 has a fantastically wide field of view that is dang clear throughout the view. Also, the viewing experience when zooming is a bit different: the apparent field of view remains constant with the 30-60WA (it's wide throughout the whole range at 66 degrees) but with the 20-70 it tunnels down a bit at 20x and kind of feels like you're expanding the apparent view a bit as you zoom in (45 degree at 20x and 63 degree at 70x). I find that the 20-70x feels more useful at 25-27x zoom because it's not as constrained/tunneled as at 20x.
The benefits I can think of are: 1) better at low light when at minimum magnification; and 2) possibly a tiny bit better resolution in the very center.
If it were me, I'd buy the 30-60WA. It would be super easy for you to sell or trade for the 20-70 (plus cash from the other guy) if you decided you wanted to go that route.
