I learned already that the quality of internet in Bangkok varies a lot between different ISP's and location.

Next month I will move to Villa Ratchathewi, 200m from BTS Ratchathewi.

What would be your choice for the Patumwan area?

ToT or True (8Mbit)?

You should first go to both service centers and check if they even have coverage and available lines for your soi.

I recently decided to get True internet for my place on Onnut, but after spending an hour or so signing papers and having them check the computer, they finally told me they didn't have any available lines for my street. I went to TOT and they set me up, no problem.

Interestingly, a couple years ago when I set up an internet connection on the same soi, I tried to get TOT. They didn't have any open lines at that time, but True did.

If both are available for your street, you should ask around the area for other users' opinions and experience. In general, I think True and TOT have about the same service and reliability. For every person complaining about TOT on this forum, you'll find another complaining about True. It doesn't matter which you chose, you'll probably end up with the same problems either way, although I have had nothing but good speed and reliable connection with my TOT 6Mb service, and the customer service was really helpful (once I got them to correct their original mistake of not assigning me the right package).

you should ask around the area for other users' opinions and experience.

Since a significant portion of the broadband experience is based on local performance it is best to speak with neighbors. (Of coursing choosing a different provider means you might get more local bandwidth. )

You may not have a choice based on the fixed line which is already installed.