I had a lift with under the muscle implants. I had the lift done twice and will go in one more time because of scaring problems. I'm one of those unlucky ones but I'm still glad I had it done. My lift was done a second time because the original wasn't done quite high enough and I had post op infection that left awful scars. The 2nd time the lift was done perfectly but I had problems with scaring again. My body rejects disolvable stitches and although I had my last surgery done in Feb, just this week I had an undisolved stitch pop out. Next time (when I get my tummy tuck done) the dr. will use regular stitches to avoid this. My left nipple lost most of it's sensitivity during the first procedure but most of it came back. After the 2nd procedure it's still somewhat numb and when my nipples get hard, the numb one is about a minute behind the other one.
The only problems I had with the implants were post-op infection during the first procedure which left some tissue scaring and slow healing of the muscle...I didn't train chest for a year after the first surgery due to pain. I got 450cc's, round, high profile, saline, under the muscle. I was a small 36D before surgery and am now a full 36DD or 38D, depending on the bra. A couple of years ago I was a 38DDD so having big boobs is natural for me. When I nursed I was a JJ cup...grrrrrrr...hence me needing a lift. I like having the implants under the muscle for a few reasons. They look and feel perfectly natural without a bra on, mamograms can be performed without problem (over the muscle they have to use ultra sound which isn't as good for detecting cancer), and my boobs won't sag with the weight of the implants like they would with overs. Mine are completely under, not just partial, do some research with your doctor, some doc's do partials but don't really explain that, then later the implants can drop.
I'd say a good way to figure out what size implant you will want is to get a bra in the size you like (you can wear a tight t-shirt and go try on bras, stuff them with socks in the store). When you're in the doctor's office, bring that bra with you and try stuffing it with different size implants. If you go under the muscle, the muscle will compress the implant a bit so pick something just slightly larger than you want.
The pain you have right after surgery truly sucks. With under the muscle implants it's worse than with overs. It's like...imagine someone just wedged a softball under your pec and the muscle is pulled tight across it. You'll also get some shooting pains into your nipples at times during the first couple of weeks but that goes away quickly. Driving is difficult and so is putting on a coat or jacket. Sports bras that zipper up the front are your easiest and most comfortable means of support for the first 2 months after surgery. Right after surgery you'll be bound up like a mummy for a few days...it feels sooo good when they take that off! Take the pain meds they offer you for the week after surgery, no need to suffer any more than you have to. I found it nearly impossible to get the safety cap off the bottle right after surgery so I stopped using it. I also used a step stool in the kitchen when cooking, I'm short and after surgery you don't want to raise your arms up very high because it hurts. You'll want someone around to help you for the first few days, but by day 4 you should be fine on your own. Most women get constipated after surgery so taking metamucil a few times a day will help. The anestessia and pain meds are what causes constipation. Shaving and washing your hair will be difficult. I have a big shower and brought in a plastic step stool so I could sit down while I shaved my legs and I'd sit on it when my husband washed my hair. Because I had a lift done, I had to keep the area dry, I don't know how difficult that is with other incisions but having some help in the shower with my hair was a blessing.
Research is your best friend. Along with implantinfo.com here's are some other sites I found helpful:
http://www.justbreastimplants.com/
http://www.plasticsurgery.org/public_education/procedures/AugmentationMammoplasty.cfm
Most doctors will give you a free consultation. Ask to see pictures of the doctor's work. I had one doc. say he couldn't show me pics for patient privacy reasons, then he wanted to do my boobs and tummy tuck together and offered a discount, then when I didn't plan surgery with him he charged me a consultation fee. I later found out that doctor messed up two of my friends, so be wary, if the doc doesn't seem right, he probably isn't. I found the doctor who did my surgery by asking my gyn for a refference and I asked around in my gym. I'm very happy with my doctor. Although I had problems, they were not forseeable and not his fault, just bad luck.