Thailand end of October diving options

Tossing up options for diving in Thailand in the next few weeks. Flying into Bangkok and have 10 days to play with (23rd October - 3rd November).

Original plan was to do advanced open water and deep/nitrox courses in Koh Tao but I’m wanting opinions and options cognitive of the fact that October is not an ideal time to be diving….anywhere in Thailand and the very limited time we have to play with.

Does anyone have any knowledge on how Koh Tao, Koh Lanta and Koh Chang compare to each other for this time of year diving wise? I know the visibility isn’t going to be great no matter what and I’m not expecting a 100% sunny holiday. My fixation is more around getting the qualifications with the least risk of course cancellations, ferry cancellations and it being 100% miserable and raining the entire day - especially with the limited time we have.

Other option is to shitcan the idea all together and head north into Chiang Mai/Pai so if anyone has any experience with that area this time of year I’m also all ears.