I've used Target Generic liquid (made in India I believe) and Wal-Mart generic liquid (made in Israel). No difference between the two. If I do decide to continue when my wal-mart runs out, I think I'll be trying lipogaine liquid, then kirkland liquid, then finally brand name Rogaine liquid. However I'm debating whether to continue minoxidil at all.
Any way, a lot of people like to debate whether foam or liquid is better. It depends on your level of hair loss. If you have a slick crown, or slick temple recession, I truly believe the foam is better. There is no hair to block it getting on the skin, and liquid on barren skin will just run down your face.
For people like me, who's hair is thick as ****, the foam is just impossible to put in. It will end up all over your hair and not on the scalp. The liquid, via the dropper, is the only feasible way of getting it to the scalp, and even then it can be tough. I've taken to using a syringe to get through the "shrubbery." Also, my hair is dense enough that the liquid never runs down my face or back of my head. I feel it slowly moving through my scalp, but it always dries before it reaches my face or back of head.