1) One big difference between, say, the 80's and today: In the past it was possible to hear most of the advanced speaker designs in an urban area, with a short road trip.
In '82 I had my choice narrowed down to three rather different sounding speakers: the Klipschorn, the B & W 801 (F, I think), and the JBL 4350 (big studio monitor that made Duke's list). I was able to hear the Klipschorn cheek by jowl with the 801 at a store in Oakland, and the JBL next to the Klipschorn in Berkeley (the Khorn sounded the most like the orchestra I heard every day, so I went with it .... the JBL was a close second, and the B & W was very pretty, rich, and pleasant, but not like "live").
Within a half hour's drive, I heard Magnapan, Bozak, Acoustat, Altec, Polk, Infinity, you-name-it. I listened for weeks (hours in each store during off hours) and came up with Khorns. It was hilarious to hear a few of the dealers bad mouth speakers they didn't carry, until I no longer found it funny, and asked them to keep their opinions to themselves and let me just listen.
Today, try finding and listening to the collection Edwinr and the others have posted!
2) The most powerful confounding variable, in the past and now, would be the combination of room acoustics and placement. I've been repeatedly surprised by speakers I am not particularly fond of sounding excellent in certain rooms. JBL 4312s sounded great at The Different Fur Trading Company (a recording studio, of course), and not too bad at Tower Records Classical. The Bozak Concert Grand sounded great (but a little tame compared to the Khorn nearby) in one store, and incredibly muffled and distant at another.