Their exactly the same solution, so technically they should be the same. But there are other factors that influence their effectiveness. Some say that foam dries too fast and doesn't get absorbed into the skin as much as liquid (which takes like 2-3 hours to dry completely). So by that, I would say that the liquid will get absorbed better into the skin.
Tho I've never seen a study as to how much is absorbed in each application percentage wise between the two, so go with what's more convenient for you. If you can afford to put on liquid twice a day and wait around for a couple hours for it to dry (and don't mind your hair being greasy for that time) then go for that, it will work better. But if you don't have that kind of time, then go with the foam, it won't make a huge difference.