For reference, I'm a 32/F( (or 34E) - fairly average 'hourglass' body type, 5'5. I sized up and ordered a large based on some other reviews I had seen (my usual size is a medium). If your unsure about sizing, I think sticking with your normal shirt/band size would be best regardless of cup size, as the material of the bra is very stretchy as opposed to the taught firm material common in most sports bras (e.g. everlast bras - which you need to origami onto your body).
First impressions: definitely not a high impact bra (though I knew that based on other reviews). Generally, though this is super comfortable. I wouldn't be doing any real sports in it, but it's a comfortable everyday bra (sits smoothly across the body). The bra's pads are not great - I found they were a bit stiff and thicker than a standard sports bra + they created a weird shape - but since it's removable it's not an issue. The material is thick enough to 'hold the girls down' so the pad's not really necessary. *The bra does provide some flattening if that's something you like with sports bras - but it's not going to minorly shrink the size down* I don't think this bra will stretch too much with consistent wearing and washing.
Overall I highly recommend as an everyday bra (I also recommend sizing based on your waistband, or sizing down if you want a very 'flattening' or tighter fit - even sizing up is fairly forgiving).
update: there is a small seam right in the centre of the bra (it can't be seen from the outside or anything) but if you have sensitive skin it will probably irritate it.