Van Halen was indeed a madman on the guitar and had a huge influence on a large variety of guitarists. However when it comes to the very "best" meaning best in terms of technique, versatility, and creativity he is definitely no where near the best. If you were to ask him to do a solo guitar concert or fill in for a big band, he wouldn't know shit and would get thrown out even if he is Van Halen. Not only that but his solos are not that diverse in terms of dynamics or melodic and harmonic variations. He is good in his own rock setting and his band, but playing in a rock group and not really anything else doesn't make one very diverse or inventive on the guitar. I could think of a bunch of guitarists who can play faster than Van Halen's finger tapping technique with nothing but a pick (and they would make it more melodic to). I don't mean to be a total asshole or anything, but I can tell you if you would listen to multiple guitarists from multiple genres(Joe Pass, Leo Kottke, Paco de Lucio,), you would definitely agree with me.