I've found that I usually run around in wraith form when solo for the stealth and incorporeal effect, which is more useful than I anticipated. However, if you have to pick just one I'd definitely say lich form as it's less specialized (it still makes you more survivable, the extra dc is nice for everything, and survivability matters a bit less when teaming).
Because the op only has room for mental toughness or toughness, which is why they can only fit in 1 form in the first place.+63 HP (why? Don't you gain +4 constitution? That is 42 hps. I seriously consider EACH wizard with at least one toughness feat)
I'd also call it +83 hp because you should definitely take at least the first two racial enhancements.