Combat base is the best against very good open guard players. I stand up to break the closed guard but I go straight into combat base afterward.
I don't want to be the puppet against a good DLR, spider guard or X guard player. There's a ton of them at my gym and staying low with a knee in the middle just mess up their game for a couple of seconds and a lot of times it gives me options for stack pass, staple pass or over under pass. Sometimes they just give me a pass over one hook to get into halfguard where I try to pass low.
I also find that torero, x pass and other ''standing passes'' end up in out of control scrambles against someone with good retention. If they sit and post on one arm, scoot, break the grips... You have no passing anymore and you're about to be stuck in a good open guard.
I still need to get better with the standing passes, because I don't want to miss opportunities, but staying low is a win-win for me. I stay on top, I get rarely swept, I have a good percentage of guard passes that works and I don't get submitted that much.