Awesome underwear I was looking for a long time to find such quality. I think it suits everyone but especially those who exercise. Similarly, I had found some at H&M but they stopped a series of climacool somehow. For the size, I went for medium while I also wear large in tight ones. The rule of thumb was that generally UA is wide like American sizes. However, even if it is large, it is stretchy so it will still fit.

The UA Tech series I think is the best I have tried.
Comfortable, flexible, convenient in all conditions/activities (gym, etc.).
The only negative is the high cost.

The 3IN ones seem more familiar but the 6IN ones are accustomed to after a while.