I would say it's ultimately about what sort of imagery you would like to record (e.g. vintage glass has an asthetic appeal of its own so you may want backwards compatability), how much function you want the lens to have (some adaptors may not give you all the auto features), how much you're willing to spend (some mounts may limit your buying options more than others), and how often you are willing to change lens 'sets' (is there any point in getting lenses for a mount that you know you'll change anyway?).

I have a Canon 550d/Rebel T2i, and this allows me a fair amount of versatility in lens choices. I have the standard modern zoom lens and Canon's own modern 50mm MkII, both of these hardly used as neither lens appeals that much to me. The 18-55mm zoom has a slightly greenish quality to it and the 50 just feels like cheap plastic (the MkI version is better but much harder to find now). I'm then able to plug in directly to this same mount EF-S mount an old crappy Sigma zoom lens, and then I have two adaptors - one for Nikon lenses (both ones that I have are from the 70-80s and are entirely manual, which is what I personally like and are my favourites) and one that mounts both a vintage Practika lens and a post-war Soviet-made lens, a 58mm which is probably my favourite of the lot.

So as you can see, I own 4 lenses that are several decades old and yet because they're all manual primes I don't ever lose anything by mounting them on this relatively new Canon body. I also like to be as hands on as possible when photographing/filming so the lack of whizz bang features don't bother me. The modern glass, my Canon lenses, do not have any manual aperture controls so if I were to mount these on a new system in the future which doesn't follow the 'rules' of the EF-S mount, their function could be greatly limited. Conversely, there'll pretty much always be a way to mount vintage lenses.

On the other side, for me, I just love the look and feel of the old glass. The fact that they're also cheap as chips is a bonus. My Soviet Helios 58mm? Cost me £8 off of ebay.

I guess all that rambling doesn't really answer your specific question... I guess the TLDR version is decide on a camera with a mount that gives you as much versatility as possible in terms of adaptors available to it or has the lens range which offers you what you want, then go for that one. I wouldn't bother getting any lenses for a system you're actively intending to change, especially if it's not a quality glass line.