This is going to be difficult, as I can only rank the Ringo albums I have (and unfortunately there are some clunkers!) but here we go:
Ringo (1973) - undoubtedly his best and most consistent album, thanks to 'a little help from his friends'.
Choose Love - A surprisingly good stab at neo-psychedelia throughout, the only let-down is the predictability of the band and the way it's been laid down.
Sentimental Journey - not one of my favourites, but a decent job of the standards.
Ringo's Rotogravure - got this for a dollar at a bookarama sale once. What I found interesting, is the reappearance of all the other Beatles just like on 'Ringo' and I love all the polaroids in the inner sleeve - it's as close to a Beatles reunion as we can get. Unfortunately the songs were nowhere up to scratch compared to the prior effort. But he does do a very good cover of 'Hey Baby'. I also have the 45 of that (with the b-side 'Lady Gaye feat. Dr John).
Ringo The 4th - This album was also found in a bargain bin when I was little.. never liked the album, maybe it's time to reassess it? It was very disco. Maybe it's time to listen with fresh ears!
I have heard bits of other albums ('Walk With You' with Macca is great, 'the title track of 'Liverpool 8' is superb, as is the new song 'Postcards From Paradise') but I guess I got a bit burnt early on with solo Ringo albums and tended to stay away from them. Any others you would recommend as essential listening? I've heard 'Time Takes Time' is a good one.