This is like comparing apples and oranges.
Jimi did more for music than Jeff in terms of putting lead guitar playing on the map, influencing many, many more guitarists, and just being a little bit more popular than Jeff. So, it makes sense to call Jimi a more influencial player.
But in terms of technique, I tend to think that Jeff has an advantage, which is even very vague. I also think John Petrucci is much better than Jimi, technically.
But they play different styles. What would happen if Jimi wanted to play faster thrashy metal and Jeff wanted to play more blues. That changes everything. But we can't compare them like that because they each play (or in Jimi's cased, played) the music they want to play. The fact is that no matter how good anyone is, they are still somewhat confined to the "rules" of their own genre. Completely different styles, scales, etc. You can't compare them accurately because they aren't playing the same style. It is like asking who is a better athlete, Walter Payton or Wayne Gretzky. You can't compare because they are completely different athletes. Put Payton in a hockey rink and Gretzky on a football field and they both would probably suck.