If these are largish companies, your previous boss will recommend you unless they just about hate you. There's almost nothing for them to lose in a recommendation, and a side possibility that you refer them into the new company later or they get to network with whoever checks on the reference (recommending a useful employee is more of an in than saying no).

Smaller companies are more of a crapshoot, since they have less room for the predictable sociopathy of middle management to flourish.