PoW is best short-term because it has been shown to work. However it is energy-intensive and not really sustainable indefinitely, so PoS - either pure PoS or else some hybrid or modified system - is the way to go in the long-term.
I think PoW is ok, but the problem is machines are so expensive and you don't get anything from them and also power consumption is very high with bitcoin mining machines than others... Can't they develop better bitcoin machines? Or is bitcoin mined so much now, you can't get anywhere if you don't invest big? Because I think mining bitcoin now is a lot of work...
https://www.asicminervalue.com/There are currencyes that uses both PoW and POS, but I think currency should use only one. By my opinion both are great, you don't get anything without work, much better than XRP.