I'm 5 foot.  about 110lbs. take a little.  I wear a 32B and it is usually comfortable if sometimes a tad bit of space.. If I wear a 32A it is TIGHT but I've worn one before alright.
That said, I got the 'small' and it fits fine.  the strap below my breasts is tight but that's how I'd expect a sports bra to be.
I'm wearing it for moderate cardio and weights so I don't normally run for that long..
I also haven't put it in the wash yet so we'll see if it shrinks.