I have no doubt the older 737s are safe, but they're still crappy planes to fly on as a passenger. Given similar cost, I'll pick an Airbus instead. It's like taking a road trip in a 1967 Mustang vs. and car from 2015. Even if you don't have any incidents, the 1967 car is going to be a pretty lousy experience as far as passenger comfort, noise, and ride quality.

I ridden on some pretty uncomfortable Airbus planes. Passenger comfort has more to do with airline choices regarding types and number of seats than model of aircraft.

Competing Airbus planes have more width, which means the seats can be physically larger. Choosing different seats isn't possible in the 737: the fuselage width is fixed. The only thing they could do to get around this is go to a 2+3 layout, and they're not going to do that because the whole reason for buying and using this plane is economy.