How tall are your speaker stands

It depends on speakers. Some speakers should be placed with the midrange at the ear level, some should be lower, some should be higher. You need to find out from the speaker manufacturer what the recommended hight is.

I've heard tweeter at ear level. Mine are 24" (Osiris). I suppose if you have home theater seats instead of a couch, they could be higher.

Its tweeter at ear level but many variables can enter in. You could have the speakers tilted up or down if at wrong angle.

Although tweeter at ear level is the general rule, experimentation can work wonders. I had a pair of Silverline Audio SR-11s sitting on 24 inch stands with tweeters at ear level. The sound was good but if I slouched down the sound was better. I moved them to taller stands which raised the tweeter about six inches. Huge improvement.
More recently I had the opposite experience with PMC DB1+ speakers. They started out with the tweeter at ear level but after some experimentation I found the sound improved with the tweeter about 4-6 inches below ear level.
Experiment to get what suits you best has become my rule.

I have found that for me 42"-44" ( tweeter height ) works best......I have 20" Stands and the tweeter is 22" ( from bottom of monitor cabinet ..It all equals aprox 42" height of tweeter ( center ) from floor .......42" is aprox ear height from my listening chair......