Songwriting: Opeth > Tool
I think Opeth's songwriting is far superior to Tool's
Creativity: Tool > Opeth
Tool are unlike anything else, whereas Opeth are influenced by many
bands, and the influences tend to show quite a bit. I wouldn't call
them the pinnacle of creativity.
Originality: Tool > Opeth
This one is kind of like creativity, so same as above.
Musicianship:Opeth = Tool
Opeth are better on their instruments than Tool is on theirs, although
Tool's soundscapes and atmospheres are great. I would say that they are
almost equal here.
Overall i prefer Opeth over Tool, as Opeth's music generally appeals
more to my tastes, but i have been listening to Tool (about 7 years)
far longer than Opeth(1 year) and i'm still not bored of them.