I have two Underworks binders, the tri-top and the 997. I'm an A-cup, sometimes B depending on brand.
The tri-top, for me, works a zillion times better, hurts less, rolls/rides up less, and is slightly more visible through clothing but is so much more effective that that feels okay.
I did have some almost unbearable compression pain for the first few days I wore it when it was new. I thought I was going to get sick or something, my ribs and lungs were so squished.
Also, it's not super-relevant to what most other people see, but I'd recommend getting black. I stained the hell out of my white one, and it's kind of embarrassing with new sexual partners.