Well I haven't had FtM top surgery, but I have had a pretty big reduction, so I can tell you about scarring at least.
Keyhole surgery does sound cool, but my chest was way too big for that. It was so big that I only had one type of surgery available to me. They cut underneath the breast (still hate that word) and then they cut from the center of that line up to the nipple, take the nipple off, remove tissue and skin and put it all back together. They also made my areolas smaller before replacing the nipples.
This happened when I was eighteen and I have good skin, so the scarring has been really good. Still evident, but not obvious, if that makes sense. My chest does not scream 'SURGERY!' but you can still see that it has happened. But the scars have healed really well and were good enough to keep my happy in under a year. They're pale, they match my skin. The ones that go from base to nipple are completely invisible, you really have to look for those. There is a tiny bit of scarring around my right nipple that is still pink, but it's not too bad. That nipple can't feel anymore either. But I was warned of these things going in and it's SO worth it.
Like Ze said, the scarring around the areolas is a dead give away of surgery, but I've never had an issue with the way my scars look.
I think...if you're a B/C you could maybe get the surgery option that was a notch down from mine (but the FtM equivilant, obviously). They just cut under the base of the breasts (sorry, I just want to be clear about which part of the chest) but they don't cut up and they don't take the nipples off. Although, for an FtM surgery they probably would need to take them off and resize them.
So anyway, three years later, my scars are very pale and I'm happy with them.
Oh yeah! And, if you go on T, perhaps you'll grow some chest hair to obscure the scars as well. :D
