I'd say they are both very similar, it is just a matter of what type of flying you would rather do. BOS 320 reserve will wind up with a lot of 3-day trips where you depart BOS between 6-10pm on Day 1, fly to somewhere like LAS/PHX/SDQ (usually it is SDQ) layover 24 hrs and work a redeye flight back, arriving in BOS between 6am-8am.

I'm not on the E190, so some others will have to chime in, but I suspect the reserves usually wind up with something like a 4-leg day trip consisting of an EWR turn and a PHL turn, or an uncommutable multi day trip that starts early in the morning on Day 1 and finishes late in the evening on the last day.

Both fleets probably fly roughly the same number of days per month, so it just comes down to which type of flying you prefer.