First of all i think it's impossible to decide the best guitar solo ever made. To many factors to consider the biggest probably being individual taste which differs from person to person.
Although i thought i might share a couple of solo's that i really like.
Metallica - Blackened 1989 by Kirk Hammet [media]http://www.youtube.com/watch?v=DU_ggFovJNo&feature=related[/media] (Solo starts at 4,32 to 5,35)
Wintersun - Winter Madness by Jari Mäenpää (2004) [media]http://www.youtube.com/watch?v=ozA234H0vFU[/media]Children of bodom - Kissing the Shadows by Alexi Laiho (2000) [media]http://www.youtube.com/watch?v=rfDZrRDmZYE[/media]Alexi Laiho just having fun (2008) [media]http://www.youtube.com/watch?v=j723qPG-qhA[/media] (Solo starts at 0,23)
Wouldn't call any of these "The best guitar solos ever" but thier original writers and performerce are among the best. If you like this kind of stuff i really recommend Children of Bodom. Most of thier songs are filled with advanced melodies and guitar/keybord solos.
Don't have access to youtube at work, but Tony Peluso's solo in the middle of the Carpenters' (yes, the Carpenters) "Goodbye To Love", and Glen Tillbrook's solo in Squeeze's "Some Fantastic Place".