For me it would be the Klipsch KPT-904. Great clean bass and articulate highs and no one wants to leave when you fire them up. 2" horn top with a two 15" woofer bass bin and 105 db efficient and even small amps would deliver more sound than you could handle and the drivers did not have to work to do it. Cello to heavy metal they did it all superbly.
What is the most FUN pair of speakers you've ever had and why?
Not the most expensive, not the best reviewed, not the biggest, but the most FUN. You know, that ONE that just makes you throw on some more music and keep listening, the one that makes your toes tap, your head bob, your ass move the most. The one that makes you think to yourself "damn, why doesn't everyone have a pair of these?" Let 'er rip.