Why do you consider Str/Cha being the worst combination of elements? I was personally going to go Str/Cha at 200

I do understand that there isn't much natural synergy between the two elements, both have hard hitting similar AoE spells. So it's just more of the same stuff. But it allows you to play to enemy resistances without losing too much damage compared to a full single element setup because level 200 Cha/Str setups are fairly strong.

Which hybrid element (or tribrid/omni) setup do you think is best for a standard Pvm setup (not Pvp)?

Obviously it depends on the team you are playing with but I'm curious about what other people see as the best pvm panda setups