There are many different ways to skin a cat.
Guys/gals with previous experience might be easier to train, however they also come with preset ways of doing things. Perhaps they will not be the perfect fit, some of the guys from ExpressJet/Compass/Trans state hated OO less than a year ago. To my knowledge soft landings will be in place once the MOAs expire, so saving a few thousand dollars on ATP-CTP in order to pay 10 year CA pay to a former 121 guy might not be the best financial way to go...