its hard to find a one all-time best band coz theres a lot of great bands out there.....different genre, style of music etc. Let's just categorize it.

Best Classic Rock Band --- Rush or Pink Floyd (hmmm Led Zep too? :D )

Best Melodic Rock Band ---- The Eagles (ofcourse, nothing comes close !)

Best Heavy Metal Band ---- Metallica

Best Thrash Metal Band ---- Pantera (Dime rules !)

Best "Hair" Band ---- GNR and Poison

Best Virtouso Band ---- Dream Theater (all instruments stand out)

Best Grunge Band ---- Nirvana

Best Alternative Band ---- Pearl Jam

Best FuNk Band ---- Red Hot Chilli Peppers and Fishbone

Best Punk Band ---- Offspring ( Greenday soon )

Best Death Metal Band ---- Children of Bodom

Best NeoClassical Band ---- Rhapsody and Symphony X

Best c"RAP" Metal Band ---- Linkin Park :D

Best Mainstream Band ------ HANSON !!!!!