In reply to marsbar:
For me, what it looks like is only important if it looks enough like a crop top for me to run with nothing else on top in the summer. If it looks like underwear then it doesn't matter whether it looks nice or not as nobody is going to see it on me. I guess the amount of shape it gives you under the shirt could be a consideration though.
I have a comfy M&S one with an underwire that I would like to wear when running but don't as the underwire stops my heart rate strap working.
Shock absorber work well on me. Debenhams and some sports shops sell them as well as Bravissimo.
I once had a scary experience in a small sports shop that had a half price sale on some over-the-head Shock Absorbers that were a size smaller than I usually wear and a different shape. Worth a try, I thought, and promptly got the damn thing stuck half on half off in a tiny changing cubicle with the only visible member of staff being a young man. I got myself out of it with some wriggling, but it was a worrying few moments.