led zeppelin and queen.
even those people who don't like these groups should be able to figure out why. led zeppelin isn't my favourite band, i've got only 3 of their lps, so that means there is plenty of their stuff i don't like. so i'm not mentioning this band because i love everything they've ever done.
its good to take a step back and view the bands without your personal preferences coming to the fore.[is that a word!?]
Yes, 'fore' is a word and the context is approriate.
I took greatest to mean the band I like the most (ELP). If greatest were to mean the most influential, I would have opted for Led Zeppelin. If it meant most popular, then it would probably be Queen who have overtaken The Beatles in some fairly recent polls. On record sales it might be Queen in the UK (Greatest Hits is the biggest selling single album in the UK), although I am not certain, and I do not know about worldwide.