Nice to meet you jellyman. I'm Cassie and I hope you enjoy it here at the Ledge.
I'll be honest: while I feel Tusk has Stevie's best songs (the others have their strong points too, namely Lindsey on Rumours and Christine on Tango in the Night), the whole album, in all it's weirdness, is quite memorable. I mean, how can you NOT forget a live performance of Not That Funny?
As for songwriting skill, they're all very different songwriters with very different styles and strong and weak points (and all 3 do make me wanna pull my hair out trying to figure out what the hell they're talking about lol), which is why I enjoy all of them for different reasons.