Opinions are like inverters. Everybody has one.
Anyway, I have a lot better long term results with the ~220AH 6V's, than ~110AH 12V, regardless of brand.
The VERY abused 6Vs in the shop are ~3 years old? Act good as new. Used to kill a like sized set of 110AH 12V every year or so, and back when we were a lot nicer to them than we are now.
I have had similar results from quite a few other systems.
I won't argue about it and did not hook up a watt hour meter... but we get a lot more hours of use at about the same loads from 2 of the 220AH 6V than 2 of the 110AH 12V.
It's a no brainer for me. Go with the 6Vs.
Also, oversize the battery bank some. If it needs 4 6V batteries, buy and connect 6 at once. Many people wish they would have done it that way.
BTW, here, Sam's has gone to 8V golf cart batteries, and the cost per watt-hour went WAY up. Dang.
They clearanced out the last of the 6V for $18 each. And I missed it. Double Dang.
G-