In Pugs tbh: do whatever u feel like it! It does not really amtter as long as teh Tank who ist MTing the Boss keeps aggro. i personaly dont really give a damn in DF stuff caus its so low tuned etc.

In proper Raid Situations: There is NO pure MT/OT ...

Idealy both tanks synergize their abilites, trying to stay out of tank stance as much as they can etc., ..... that MT/OT mentality however deos not apply in a proper Raid situation.

having the mentality of beeing pure OT/MT depending on your role is kinda wrong in this game