I agree with the others, it's an hour hop so more or less the same. I'd go with whatever is most convenient (airport wise) and since I live in West Bangkok, there's very little difference between going to DMK or BKK, but for someone who lives/stays in Central or East Bangkok, PG is definitely a better option and in that case I'd even pay a thousand or so more just to avoid taking a taxi up North.

FD is certainly annoying when it comes to carry-on limits, sometimes they check and sometimes they don't; and sometimes they enforce rules arbitrarily. For me it's not really about the money... it's about having to be pushed aside, getting your cards out, pay and wait 5-10 minutes for them to process the payment, signing the receipt, slowing down the boarding for everyone else, etc. I've seen this happen more often than I'd like to. It's just not fun.