I don't think symmetry matters at all for this sort of 'biner. The three things you will notice are gate opening, basket size (how wide the wide end of the 'biner is), and cross-section. Larger gate opening and basket are nice, although with skinny ropes like you are talking about I think anything on the market called an HMS will be fine. The cross-section will effect the gripping power of both belay devices and munter hitches, with smaller equalling more grip.
I'd say that the Petzle Attache' would have the least grip and be the biggest everywhere else. The camp, Black Diamond Vaporlock, and DMM Sentinel would all work fine. All of these are hot forged. If you just use them for alpine you'll have them forever. If you do a lot of rock climbing and rappel on old dirty ropes they will wear out in a few years, noticeably faster than big fat HMS 'biners. I've been very happy with my vaporlock's for this sort of use.
I've never found the need for a supermunter, I can only see using it in a rescue-lower or rappelling with a really thin bit of accessory or tec cord. I would highly recommend the DMM Bugett for rappelling and belaying with skinny ropes in not-so-technical alpine situations, and some sort of autoblock-type device if you are pitching out anything very steep. The weight is more than offset by the efficiency and energy saved by having easy-to-use tools. The cost will be saved quickly in rope wear, the munter is not kind on ropes.
Braced body belays are the fastest in many situations and are commonly used in guiding. They should be practised if they are to be safe. If you are building an anchor than that will take much longer than loading your rope into a belay device, and with practice that is pretty much as fast as the munter hitch.
