That's what I was thinking--this question is a false choice, since when you buy a PoS coin to stake you're investing in that coin.  Not quite sure what OP is asking in that case.

PoS coins aren't very popular on this forum from what I've seen, but I happen to think they're pretty cool.  The main problem I see is that there's no barrier to entry as far as someone wanting to create his own staking coin, and so far the result of that fact is that there are quite a few of them on the market.  To me that means a lot of them likely won't be able to maintain their value over time--and the same could be said for many altcoins in general, whether PoS or not.