@Wayne ******
the non-O would give a better chance of opening a Thai bank account. The other difference is not needing to do the extension before day 60. Not a lot else difference if strictly sticking to 2 trips of 3 months or, 1x 6 month block a year in Thailand. Go beyond that and amount of time and you can eventually start getting questioned at entry. Some airlines will require proof of return or ongoing flight ticket with the tourist visa route.