You would be stamped in for 60 days every time that you enter Thailand on a valid METV.
Note that each entry can be extended by 30 days.
What type of visa you opt for depends a lot on your long term plans.
If indeed you plan to spend significant time in Thailand every year then a Non O retirement with subsequent extensions and reentry permit could be best option.
However that requires you to maintain funds in Thai bank or use agent.