It really depends on your area. With us, sometimes things would take days to get here when it shouldn't have and others get here faster then I expect. I picked express because frankly, our USPS sucks.
If you feel like your USPS is great, then go for it. I think it helps that it's in the US so it doesn't has as far to go, mine came from Thailand!
Oh and btw, beautiful Betta!