[Vampyr]

Snow is the best sentinel, his HP becomes ridiculous.

Fang has a crazy strength stat though which, as you said, helps her be a great commando as well which I think makes her a better fit for a well rounded party. You can use Delta Attack to work up the stagger gauge to about 40% - 50%, then switch to Mystic Tower (Ravager Sentinel Ravager) to stagger. Flip to Relentless Assault to work up to about 500% damage (on the bigger guys), then flip to Commando Commando Ravager to do some crazy damage.

So yeah, Snow can be a great tank, but having someone who is a good commando is also important in a lot of fights so that's why I opted for Fang over him. Lightning is there because she's just good at everything, though perhaps not great. She's a good Ravager, a good Commando, and a good Medic.