Prot can pretty much solo most stuff without gems so it's up to you what you're after... faster kills or more pulls?
Straight STR gives better DPS and bigger heals, so that's a plus.
2/2 STR & stam is more efficient and a better "oops" insurance, so that's a plus.
2/2 STR & haste gives cooldown reduction on many abilities, so more DPS and quicker HP generation... so
that's a plus.
It's all got upside, just up to you what you want. "Best" isnt always cut and dry... I used talasite gems before the nerf cuz pally DPS is pretty OP already, worked great. Also had one with 2/2 STR & stam... also worked great. Cant say I could say which is "better" cuz both killed stuff as intended.
I will say that single-target is the weakest part of the dungeon solo so you can choose to focus on improving that OR you can focus on bigger pulls to get to those 1v1 fights faster and save time that way... point is, I'm not much help here.