Love the stuff Dio recorded with Rainbow, in particular Rising & Long Live Rock ‘n Roll, bit more filler on the first album I feel. Stargazer for me is probably the pinnacle from those albums, and possibly of both Dio and Blackmore’s careers. But I’m hard pushed to say that his albums with Rainbow are better than those he recorded with Black Sabbath, particularly the first two, Heaven & Hell and Mob Rules.
As much as I love the solo stuff, I don’t think it quite compares with those two bands, though maybe that is because he released so many more solo albums and the quality diminished a bit after the first three.