I would go to Bangkok as a first timer. Bangkok is simply more fun. There are more sights to see, food to eat and plenty to explore.
I find that most thai will have some tattoos but not all are heavily tattooed. Unless u totally can't accept any form of tattoos, otherwise u should have plenty of choices.
I find hotels in Bangkok are generally very affordable even around silom. Personally I would stay in a hotel rather than an Airbnb.