I think you can't just give an accelerator the binary label of good/bad.
Sometimes different alumni have very different experiences. Sometimes an accelerator's niche is very relevant to one company's problem but not another's. As Sam's advice said -- it's more useful to qualitatively talk to someone you know (and also trust, or at least consider credible) to evaluate their opinions on the accelerator. There are too many unique factors.
Obviously, this is hard for a new-ish (pre-) accelerator, so one heuristic I've used instead is to review the experience of the accelerators' founders and mentor network. It's a start.
Sometimes different alumni have very different experiences. Sometimes an accelerator's niche is very relevant to one company's problem but not another's. As Sam's advice said -- it's more useful to qualitatively talk to someone you know (and also trust, or at least consider credible) to evaluate their opinions on the accelerator. There are too many unique factors.
Obviously, this is hard for a new-ish (pre-) accelerator, so one heuristic I've used instead is to review the experience of the accelerators' founders and mentor network. It's a start.