Adrian Smith.
I've never been wild about metal guitar solos taken as a whole. A lot of them don't really stick in my head. They can be good solos, but they won't necessarily stick with me, especially if they're fast and shreddy. Granted, there are exceptions. Marty Friedman occasionally turned out an excellent solo, as did, actually Kirk Hammett. Yeah, he gets lazy, but the One solo is pretty fantastic. Tony Iommi, obviously, played some quality guitar solos as well.
Obviously, if we're counting DT in here, Under A Glass Moon has a stellar solo, as do many other DT songs such as Breaking All Illusions. Including DT, my favorite metal solos would probably mostly be Petrucci, starting with UAGM, BAI and the solo after the F# in LTL.
But leaving DT and prog aside for the more straightfowardly-heavy metal artists, there really are only a handful of soloists who do it for me. I love the Iron Maiden guys for sure, and all three would rank among my favorite metal guitarists (sorry Dennis Stratton), especially Adrian Smith and Dave Murray (sorry Janick). I would name Janick's rendition of the Hallowed Be Thy Name solo (at its best) as one of his best solos, and for Dave Murray I would name Sign of the Cross as my favorite of his solos.
Adrian Smith, of course, is indisputably (/hyperbole) the best Iron Maiden guitarist and also the best guitarist in metal. Adrian Smith plays many excellent solos, but Stranger In a Strange Land is probably Adrian Smith's best solo. His two Seventh Son of a Seventh Son solos are also noteworthy, as, naturally, are many many other Adrian Smith solos.