The marriage visa there is alot of extra paperwork involved ok it's 400,000 in a Thai bank that is required the retirement visa is 800,000 Baht in a Thai bank but alot less paper work.
If you can afford it I would go the retirement visa as you are more independent on that visa which ever you decide you will also need a multi re entry visa that is 3,800 Baht and you can go in and out as many times as you won't while your yearly visa is valid