Definitely the best of the lot.
Ultima V is in my opinion the absolute pinnacle of Ultima. The system that it designed, being the tile-based system, reached perfection in this game(no, didn't think 6 was perfect). And in my opinion, the graphics still stand out as being good by today's standards - solid, not dated, and they created a motif that is still hard to bash. Everything that began in Ultima IV was made better in Ultima V, and it got me hooked. Of course no one will ever believe you when you admit these things, but just try it.... and you might just agree.
Nothing. Absolutely nothing bugged me about this game. I have always thought, and still think, it's a perfect roleplaying game.
The Bottom Line
It's the most quintessential of the Ultima series, and shows you everything that made the Ultima worlds so detailed and made the game design groundbreaking. And the graphics are still bearable, even today. Perhaps it's not an immersive enough experience for people brought up on the 3D revolution, but for those of us who began before that time, this is a classic roleplaying game. Absolutely my favourite, and still the best of the Ultimas.