Man, Varian has so many good talents. It's legitimately hard to give some of them up.
Even trying to build him as a full tank, the choices get somewhat hard for me.
Level 1: I'd love the extra slow on Lion's Maw, but I think both the others add too much more damage to give up. I think I prefer Overpower here, even when tanking - you're going to be relying on your W anyway, may as well get a lot more damage out of its use.
Level 4: Shield Wall is unquestionably the full tank talent, but damn, Warbringer is tempting. Basically a choice between huge mitigation for a bit more initiation/peel.
Level 7: Probably the one tier I don't really care for. I think you either have to go for Second Wind or Victory Rush, and one is probably mathematically just better (though I don't yet know which one).
Level 10: Obvious one if you're tanking - take Taunt.
Level 13: Banners! Probably either Ironforge to make yourself and teammates even tankier or Dalaran if you have some big AP allies. Probably Ironforge though.
Level 16: Probably Mortal Strike for most situations, but consider Shattering Throw for Tassadar, Zarya, Artanis, etc
Level 20: Vigilance seems okay, but might be great (maybe against fast AA heroes like Tracer make it really good?), Glory to the Alliance also seems really strong, but then so does Demoralizing Shout. Guess this one will depend on your comp and enemy comp.
Clearly Varian having a tough choice between his talents and lots of situational decisions is the point, and that seems to have been accomplished. I feel like his numbers are going to get tweaked a lot though, as some of it feels really out of whack.