a = long, b = short.

the 9-hour, i don't think, is very senior. it only guarantees 72 hours vs 76 for the b, plus the company can take it away from you twice without any increase in pay. all in all, not a good deal unless you commute from a short distance. if you live in LAX, it's not going to allow you to sit EWR or IAH reserve at home. if you live in SAT or DFW, and you're IAH-based, it will probably work for you since you can drive.

IAH is the most senior base. the bottom 737 FO lineholder in Feb is an april '05 hire.