the best speakers i have ever heard are made by either naim or linn.
obviously, big speakers tend to sound better than small, if the source material is substandard, the preamp isnt too good or the poweramp hasnt enough headroom to cope with the required listening level or cannot properly drive the speakers, then bigger or betterspeakers cannot improve the sound. i personally advise being wary of ported or long throw or bass reflex type designs for rock music, because i think what they gain in low end frequency tresponse, they lose in punch and clarity, particularly with fast, repeated notes like you get played by a typical hard rock bass player. if money isnt an issue, then consider a fully active system... this is a particularly noticeable improvement when using small/midsize speakers. i am talking about using an active crossover system, tunable to the listening environment at least here.
my personal favourite setup was a linn kairn preamp, linn klout poweramps, linn isobarik aktiv speakers. for asround £2500 secondhand, that setup will blow you away, man!