boil kettle

I am resarching a new boil kettle and am wondering if i better off with a skinny tall or wide short? I have searched the forum but cant find anything on this, although im sure its been discussed. Im looking at 15 or 20 gallon pot and now i do BIAB but am considering changing my system up. I have never heard anyone say i regret buying such a large kettle!!!

Wider = more boil off. The magic ratio, from what I hear, is 1.2:1. Northern Brewers kettles prominently display that.