there are statistically more complications with bypass, but complications with either surgery are really pretty low. The rule of thumb lately seems to be if you have GERD issues, go with bypass, otherwise, it comes down to personal preference. They're both good surgeries, and you'll find people on this site who've been very successful with both.
you will have to take vitamins for life with both surgeries, but there are more consequences if you slack off on vitamin-taking with bypass because of the malabsorption. But if you're diligent about taking your vitamins, then vitamin deficiency is rare.
about 30% of sleeve patients develop GERD (or if they have it prior to surgery, it can get worse), and about the same percentage of bypass patients (about 30%) experience dumping syndrome, and in both cases that's kind of a crap shoot. You can't really predict ahead of time if you'll get those or not (although if you already have GERD, it's very likely not to improve and there's a decent chance it'll get worse with the sleeve. On the other hand, bypass usually improves if not outright cures GERD). If you have bypass and are one of the 30% who dump, it can be controlled by not eating a lot of sugar (or fat - some people dump on fat) at one sitting.
hair loss is very common with both surgeries. Actually, it's a potential side effect of any major surgery (and childbirth, too), due to stress on the body. I think we see it more after bariatric surgeries than other surgeries, though, because in addition to the trauma from the surgery, we're also taking in very few calories the first few weeks/months. The good news is, it's temporary - the hair will grow back - and in most cases, you're the only one who'll notice it. A few people don't lose any hair at all, a few lose noticeable clumps of it, but most of us are somewhere in the middle. It's more like "shedding", and it's not enough for others to notice. I didn't lose much at all. It lasted maybe three months and then started growing back. But anyway, don't make your decision based on hair loss, because that's very common regardless of surgery.
I don't think you can really make a wrong decision either way. I'd take into account what your doctors say, and also consider your personal preference. Some people are more comfortable with one or the other. As I mentioned, they're both good surgeries and you can get good results with either one.