Pretty minor differences between JFK/BOS 190/320 for junior lineholders, but drastic difference between what it takes to be bidding 50% among lineholders in base/equip. If quality of life is important then the E190 might be the best way to go.

BOS E90 FO
50% lineholder #~2330
Junior lineholder #2654
Junior pilot #2939

BOS 320 FO
50% #~1980
Jr line #2786
Jr pilot #2932

JFK E90 FO
50% #~2400
Jr line #2708
Jr pilot #2940

JFK 320 FO
50% #~2040
Jr line #2763
Jr pilot #2937