If you just look at the printed words on the page, I think he's among the best, but I don't know if he's any better than Bob Dylan, Leonard Cohen, Lennon-McCartney, McLennan-Forster, and the rest. To be honest there are people like Paul Weller, Mark E. Smith, Jarvis Cocker, and Paul Heaton who-- over the course of their entire careers--have written more interesting lyrics.
The trouble I have with the question is that it seems to imply a comparison of lyrics only. I think his words have to be considered alongside his singing, and his singing is really his total vocal delivery: Morrissey has some of the best hums, whines, moans, laughs, and "la la la"-type utterances in the history of pop music, none of which are proper lyrics. And then there are other important factors, all of which I'd sum up under the word style (performance, charisma, media presence, clothing). When you put it all together, yes, I think he's the best. Without question the best of the last thirty years.