What is better? back only inflating, full vest inflating, or ???
Hard to say one configuration is truly 'better'. There are reasons why it may be a little easier to achieve good horiziontal trim with a back-inflate BCD, and you will see comments from a numbers of divers who prefer back-inflates for that reason. But, a competent diver can achieve good trim with a vest as well. I have a vest, a back-inflate, several BPs and wings, and a 'soft' plate / wing (a TransPac), and I am comfortable when diving each of them. I personally prefer a BP/W for simplicity and versatility, and suggest that approach to new divers considering gear purchases, but it is a preference rather than an absolute endorsement. I also prefer a weight belt to integrated weights, and I think many of the issues that some divers experience with back-inflate BCDs occur with integrated weights - a bit too much weight, usually positioned at the diver's front, and associated overinflation of the bladder, at the diver's back, resulting in the face-forward sensation that you see reported as a problem with back-inflate units. It doesn't have to occur. I also prefer having a crotch strap, which is a little harder to come by with a vest unit (unless you rig one yourself), and some back-inflate units for that matter.
I have a friend who has a Mares Syncro tech back inflating bc, said he'd sell it to me. Any suggestions, info, or what to stay away from would be greatly appreciated.
Reasonable BCD. It is weight-integrated, but you don't have to dive it that way - you can still use a weight belt with a weight-integrated BCD. Positives - it has received decent reviews, will easily meet your needs based on the description of the diving you plan to be doing. Negatives - we have had a few challenges at the shop (we are a Mares dealer) with getting parts for Mares equipment in a timely manner (I use a Mares reg for pool work, and find some replacement parts hard to come by), so I generally stay away from Mares, except for their fins (and my used reg), as a result. I wouldn't buy a Synchro Tech new - way too much unnecessary padding that adds to your weight requirements. But, for a used unit IF the price is right - which would be no more than 50% of the lowest on-line price you can find for a new unit - it should be a good starter BCD for you, and for the type of diving you plan to do.