From what I understand, if you’re using a Strat type guitar, into a Fender type amp (SRV, etc), Tubescreamers are pretty much a go to. However, if you’re using a Humbucker equipped guitar into something like a Marshall (Satriani for example), the EQ bump from a TS isn’t where you want it, you’re probably better off with something like a Boss OD1. All depends on what tone you’re going for.