What is the best part of Thailand to visit in October and November regarding weather?

I think the only place to avoid is smoke season, in northern Thailand. Everywhere else, every time else, is fine.

November is actually very nice and cool in Bangkok area, and on down past Rayong etc. The rains have pretty much stopped.

Most of the north should be rain free and cooler.

North-the norther the better😊

A lot of people think the “wet season” or “monsoon” will be constantly raining. Usually this is not the case. You could be unlucky and get a day or so - or even a week of constant rain, but normally the rains are short sharp showers that last an hour or so and then the sun comes back out.

Thailand is a big country and weather patterns differ from place to place. In many places the weather is incredibly localised - so much so that it may be raining on one side of the city/town/village and completely dry on the other.

Traditionally the wettest months are :-

Bangkok, Phuket & Krabi - September & October

Chiang Mai - August & September

Koh Samui - October & November

Online weather sites or weather apps almost always show rain/thunderstorms during these times and freak loads of people out by making them think it will be raining all the time. They show that because it “could” be raining or a thunderstorm at some point during the day. There probably will be, but probably just an hour or so. Some apps are better at predicting than others. A paid app like Ventusky gives you a “satellite” type image of what may happen. It’s not always correct but way more so that the traditional apps or Google.

Usually it's very hot so a lot of times the rains are welcome as they cool everything down a few degrees.

Sometimes during the monsoon period the seas are rough and might impede trips to certain islands. You're better off to wait until you are here to book island trips a day or so before so you can guage what the weather will be like and choose an alternative if needed.

Be VERY wary of swimming in the sea at these times of the year. Big waves cause rip-tides that unfortunately lead to many casualties every year. Best to stick to swimming in your hotel pool

Generally up north would be a lot cooler at that time of year.