I use regular bubbles. The cat doesn't really ingest any.
I tried the catnip bubbles, but they were oily and heavy and hard to make bubbles with... they smelled awful and chemical-ly and neither I nor the cat liked them. Simple soap bubbles seem safer to me.
Not all cats like the bubbles, regardless of the kind. Odo is terrified of them and leaves the room whenever I open the bottle. Zek, however, stomps on them. I've used both catnip and regular bubbles and never noticed any ill effects from either.