What we would run for our tanks we used for team ranked on pot5 (full tanks not hybrid tanks as those are another beast entirely) is get yourself up to about 40 k health, then we would start stacking defensive stats via augments, that way you have the health to survive teams that run dot cleaves and aoe cleaves, but you have the defensive stats to make surviving with a dps on you a little easier.
Some people would have 2 different tank sets, depending on what type of team they'd go against they would swap out sets, I just used one set built as I described above, just because I'm lazy and hate my juggernaut.
I don't know a whole lot of tanking regs because I don't do it because it's boring as hell, but from a tanks perspective, you generally want to guard the guy that is taking the most damage from a high single target class such as marks sniper deception sin carnage mara ect, or if you're not bad at the game, you can put guard on one person who is really taking the dick, and you can sit on the carnage mara or deception sin or whatever the single target class is and peel them off whoever they're on. Like I said I don't do a lot of tanking regs because frankly it's boring, but from the few times I've done it (mostly from a dps hybrid standpoint) that's how I do it. Oh and ppl in my group get guard priority over some random.