The answer to your first question is yes, smartthings does not provide a migration tool for devices so you have to exclude your Z wave devices from your old hub and then include them to your new hub and re-create all your automations. Annoying, but it’s a one time event, and you would have to do exactly the same thing if you bought a competing brand of hub.
As far as competitors, there are other competing hubs which may have a more stable zwave implementation. Especially if you stay under 50 devices. Every system has its own pluses and minuses which is why they are all ranked about 3.5 stars on Amazon. There’s no one clear winner, it comes down to what your own priorities are.
If you only have Z wave devices I would definitely consider a Z wave only system as it is likely to be more stable then a multi protocol platform, particularly a cloud-based multiprotocol platform like smartthings.
I wouldn’t go with Wink for multiple reasons (I do have one, but use it very little at this point). First, it seems pretty clear that the company is facing significant financial challenges for the third time. So I’m not sure how much future it has.
Second, it’s also a cloud-based multiprotocol system, so you run into a lot of the same issues.
But many of the Z wave only systems are older and don’t have a really well developed mobile app. So that’s a separate consideration.
One option to consider would be Abode. It is also multi protocol, but runs locally. Very nice app. Doesn’t support as many different devices as smartthings does, but appears to have better reliability. I would certainly choose it over wink at this point. It also has nice video integration.
But there are just a lot of different factors involved. (Also, since you didn’t specify, I’m assuming that you are in the US or Canada. If you are somewhere else, then the device options might vary. In particular, Devolo has a nice basic Z wave platform for Europe.)