What is the most FUN pair of speakers you've ever had and why?

Thiel SMGa speakers driven by Braun/Atelier ADS A2.  
These were my first "Audiophile" grade speakers.
And you might say they were my first love.
Purchased together with the ADS A2 in 1984.
Traded in in 1996 for a pair of Thiel CS .5 speakers after my son was born and my wife and I were afraid that it would be much too easy for our baby toddler to knock over those baby Maggies.  Hence the baby Magnepans were traded in for a pair of baby Thiels.
Still have a special fondness for Maggies, as well as for Thiels.

Great thread.

I think maybe we have so many "past" speakers is we just had more fun when we were young, I know I did.

I would say Silverline Sonatas. I had them for several years and they were very dynamic and easy to listen to.

If they would still be “the most fun” why have something else?  

Good question, and I have thought about this many times.  There is an argument to be made that the most fun speaker is the one you should keep.  I think for many responses including my own, it's a question of weighing fun factor (big bass, slam, warmth, etc) vs refinement.  Also there have been many responses of speakers with big woofers, maybe there are folks who no longer have room for large speakers.

I owned a pair of Klipsch Heresy's way back in 1981. Ran them through a Luxman Integrated Amp with a Nakamichi B2 cassette deck and a Denon turn table. First real system while in the Navy. They were GREAT party speakers. Every year in May we had a big beach party, rented a generator and had music. Sold them to a friend in 2005. I still hear them at his house every now and then. I have definitely upgraded, but everytime I see and hear them they bring back GREAT memories. 

Large Advents. I truly grew up with them! Still have a pair tucked way in original boxes.