I'm not sure the comparison is apt, although I see where you're coming from. As much as I like the project, it seems pretty clear that ADA is quite overvalued right now. But it's not pumping like crazy like XRB is... ADA is up ~7x in the last month, XRB is up ~125x during that time.

Also, the two coins are fundamentally different. XRB sells itself purely as a currency, while ADA doesn't even have the stated goal of being a currency. Cardano's entire purpose is to see what creating a blockchain using the scientific method looks like. It tries to identify and correct the technical issues faced by previous blockchains. It's really not trying to be a currency - Charles H has even stated in interview that one of the cool things he'd like to see come out of the project is a developer creating a volatility shielded currency on top of Cardano.

So to me, the long-term aspects of both coins are really not comparable. I ADA is currently overvalued a bit but as a 2019 pick I'm quite confident it's solid. Can't say I feel the same about XRB. If I had any I'd be selling them all pretty soon.