Depends on if you're collecting your bags and going through immigration. If your bags are checked all the way to Phuket, then it's Phuket. Otherwise it's BKK!
With Thailandpass you can check in hotels, rent cars and motorcycles, show to the cops, impress the bargirls, charter boats and so on! Thailandpass is a good investment and lets you stay out of trouble even if you stir up trouble!
The problem with most banks is, they want to sell you an insurance before they'll open an account for you! It took me two days and around six branches! It takes at least 45-60 minutes for each bank to aske this one question, because you have to get a ticket and wait in the queue! After 4 banks I had enough and left it to the next day! In the end, Siam commercial opened one for me without any problems!