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

@larryi pure gold, thank you!

If you like to waste money buy passive speakers, amps, and cables.

If you like to save money buy active speakers and power cords.

You have to spend at least 3X more on passive to get the equivalent result of a good active so I prefer active speakers.

By dynamic linearity(my handle) which is NOT playing loud cleanly although that's a small part of it. It's accurate, non-compressed level changes whether they are micro changes or macro changes. It's what makes live music sound live. Think of it you can tell live sound even outside a room so it's not the standard ideas such as flat response which is lost out of the room. And change a seat in a live concert and the response changes in different locations but the dynamic linearity doesn't. I think of wide bandwidth speakers that always sound sweet and smooth as wide bandwidth radios but not as accurate reproduction. And all the other stuff like flat response and low distortion matter but they are secondary.

Natural unforced sound.  

Sensitivity, I learned this the hard way. Power an 86 db speaker with an outstanding 30W class A, no bass at all, and lifeless. Then power them with 600W monoblocks, audio nirvana!