A BC really has two basic functions: It should hold the tank in a stable position on your back, and it should provide sufficient flotation for the kind of diving you do. Both of those things are extremely important. A BC that does not fit well, or does not stabilize the tank, will make your diving life miserable. I prefer a BC that has SOME kind of rigid component to it, like a plastic or metal plate, to provide a stable platform for the tank, so it cannot slew much from side to side. All-fabric BCs allow a lot of tank movement.
The BC should cinch down around you to a degree which is somewhat uncomfortable on land, because any exposure protection you wear will get a bit smaller underwater . . . I like crotch straps, because having one means you don't have to have the shoulder and waist straps quite so tight, to hold the whole rig in place.
In dive gear, simple is often better, just because salt water is hard on things. Everything that moves can (and eventually will) fail, so for example, having a whole BUNCH of dump valves really isn't better than just have one you can operate when you are horizontal or head up, and another you can operate when you are head down.
BC makers often like to put all kinds of bells and whistles on their gear. But how something works on land (wearing it around in the dive shop without even a tank on it) is very different from how things work in the water. Pockets that look like great ideas can be all but impossible to access while diving. Tons of D-rings may look like a good idea, but if you put things on all of them, the things may get in one another's way, be difficult to locate and deploy in the water, and cause you to resemble a poorly decorated Christmas tree.
Dive shops often try to steer folks to their highest priced items, because the margins are better, and because manufacturers REALLY want them to sell those things. Do not be persuaded. Whether it's BC's, regulators, or anything else -- a new diver should start with modestly priced, basic equipment. If you find that you are doing 175 dives a year, you may want to trade up on some of your original choices. That's okay and unavoidable. But worse is spending a thousand dollars more than you needed to for starter gear, and then discovering you do six dives a year, and don't even particularly like the equipment you have to do them.