I use them both and there are advantages to each.
The main advantage to the shapton glass stones are:
They're splash and go (require no soaking)
They're hard (easier to learn on with less gouging issues when you wobble)
They wear more slowly (less dishing)
The Imanishi set with the beston, bester and rikas have these advantages:
They have better feedback
They are less money
They're much thicker so even though they wear faster they should last longer (I think)
Personally they're more fun for me (don't ask me why but I enjoy using them more for some reason)
So, you won't go wrong with either set. Don't spend too many brain cells on the decision.