Well, personally I think Spanish Fly is a fuckin bad ass solo. It's so awesome.
Only thing is there's an actual correct transcription/way to play it. With Eruption, everyone does their own thing and I really don't think there is one person out there that can play this perfectly. Not even the man himself can do it, and that's why he changes it everytime he plays it live (some of the changes have been fuckin bad ass, watch the Pensacola bootleg vid). It's a fuckin great tune and I think Eruption is just a better solo than Spanish Fly, and only for that reason... because no one can play it correctly, lol. I'm sure there are a few exceptions, but what I'm really trying to say is that Eruption is so crazy, and Spanish Fly is a more prefect and "anal" (as in it's not Ed's usual style of going nuts over the fretboard).