It seems like cacti is more popular than cactuses, or it is getting more common, at least it´s what transpires from searches on The Economist, the magazine People and Youtube. It often appears also on The Sun and BBC.
Anyway, not even the grammarists or the grammar buff people don´t agree much, some would say that cacti to form the plural of a "group of cactus" of the same species and cactuses to the colective of cactus, but being of different species.
Other would say that they favour "cactuses" (as a regionalism); e.g. In Australia.
Sometimes it goes with the personal style, and there are people that advocate cacti as being more proper to written, and cactuses to spoken English. It seems like this is right, at least from the following Youtube video where the guy says cactuses and write cacti. But then, he could be referring to the different species...
Well, I will leave this at that, thus I agree with NeyF, it´s the sensible thing to do.https://www.youtube.com/watch?v=XHvpSG207lQ