I started with BidNav 3 years ago and found tremendous value in it. Last year I switched to the ALPA program from August-December and I was less than impressed. In January of this year I went back to BidNav as I had went to a different fleet with different seniority. I can't speak to the other program (ZedSked), but I'll try it out. Bottom line is for me it's worth the monthly price to use BidNav.
As an aside, I won't be trying ZedSked until the January bid period. Too many important things going on in November & December for me to risk it.