Which Spread to Use for Highly Speculative Bonds?

As seen in many threads on the forum, CFAI points out that “OAS has limited use in the analysis of speculative grade bonds because default risk is excluded from the calculation”.

I think I understand that sentence after having read through the threads here, but that begs the question:

If OAS is not appropriate, which spread measure is appropriate for speculative grade bonds? Thanks!

What about credit spreads?