the big one: how do you choose speakers? By what features, data?

@grislybutter , If you want to get serious I need to know how much you are willing to spend, the size and layout of your listening room and what kind of music you like. 

@cey great pointers!

@mijostyn dead serious! 

budget 2K - used?

room is 15x12 one corner is open but seems to be ok

I like sweet vocals, not a lot of bass, clarity, details but not too analytical, warm sound

Imaging is preferable, my current speakers are 4 feet from back wall, 3 feet from the side, I am sitting 5 feet from the speakers. I am wearing a yellow T-shirt :)

@grislybutter My 911 is Yellow! 

If imaging is your priority and with your situation there is only one way to go, The Harbeth P3ESR XD. Put them on stands exactly where yours are now and enjoy. Later you can add two subwoofers to the mix with a two way crossover. This lowers distortion in the little woofers of the P3 and raises headroom to an astonishing level. Close your eyes and you could easily imagine you are listening to a Magico or Wilson loudspeaker! Not Kidding!

I am wearing a Grateful Dead T shirt. 

@grislybutter

I go by...

1. Have I heard it and like it, with amplification I’m familiar with?

2. Looks, do I think it looks good?

3. Porting and placement, where will it (can it) go?

4. Specs last for me.

I have worried in the past about recommended watts/RMS before regarding speakers but haven’t been disappointed when I’ve kinda pushed the limits of a few speakers I have.

Happy hunting and good luck!

The only measurements that I find of any value is the impedance the phase angle. A flat impedance curve with minimal phase shift makes for a very easy load, opening up all kind of opportunities with amplification (think single ended triods for example). A impedance curve that has lots of low drops and especially when combined with significant phase shift is much more difficult and requires an amp that can handle this (think old Krell or current Gryphon amps).

Then the sensitive comes into play. A very easy load with high sensitive (Zu Audio for example) makes it a perfect match to low power amps and as a matter of fact (and personal experience) might not work well with a high power amp (in my case, the volume control of the integrated amp was simply too sensitive to either it was too loud and one click lower and it wasn't loud enough). Low sensitive combined with a difficult load and you will need a monster of an amp with lots of power, but even more so lots of current.