There is a lot of choice available in Thailand for coffee drinkers. No one place is king for me. It all depends on what I want at any one time. I have my favourites and there are some places I go to occasionally.
I go to Starbucks occasionally. The good thing about them (if you like their coffee) is that the taste of their coffee is consistent. The downside is that it is expensive for what you get. I have had much better coffee cheaper in several places, including a speciality coffee shop but it really wasn't worth the wait there (weigh the beans, grind the beans, weigh the ground beans, measure the water, weigh the output, time it to the second, etc) .
I quite like the taste of 7 eleven fresh coffee (30 baht for a latte) and it's convenient. Fresh coffee in McDonald's is OK. Amazon is mostly OK and fairly consistent. Independent shops, you never know until you try them, but that can be fun and can turn up some gems as well as duds.