I think it all depends on where you're moving from and to.

I wouldn't want to be an AA mid-tier elite in DFW, CLT, or PHX, nor a UA mid-tier elite in EWR, IAD, DEN, or SFO (where even 1Ks are sitting in middles).

Many have opined being a mid-tier elite in a non-hub city is always helpful, so being a UA Platinum where AA is huge (PHL is a good example) is nice.