Better trips is subjective to each pilot. Average time per day is roughly the same for each. Both cover all three airports. Pretty much the only difference is that the 737 has taken over the Caribbean flying from the 320. But that doesn't mean the 320 couldn't do it in the future.

Right now the 737 is the "growth" aircraft in DC since it is a new base. The plan is for each fleet to be roughly the same size, so the 737 needs to grow to equal the 320's current size of roughly 130 F/O's. Based on the last vacancy bid, they are just about there. (90 vacancies advertised). However with senior pilots bidding off due to upgrades and base transfer, expect more vacancy bids on each going forward to maintain that ~130 pilot base number.

DC