Classic and Core, both of them are good. If you are using Core, you should stick to it. Thats what i recommend.
In the long Run, both will be equally better and important.
in the long run both will adhere to the same protocol (what ever that happens to be 2MB blocks or segwit-ed blocks).
there will be no forking off.
If both of them are same in the future, would it will be better to combine the feature of both .
Means both of them using the same protocol and same block size.
It will be better.
right now they are both pushing very different things.
2MB vs segwit
right now it looks like core will win with segwit.
but let's say in 3 months segwit is not ready and still no where near ready
miners might get fed up and go with classic.
core will have no choice but to go alone with this, but they will still work on segwit and it will probably still be accepted by miners onces its ready.
so you might be right they might get combined.
its up to the miners to pick and chose which feathers they want and when they want them
core and classic only make suggestions.
competing implementations dont just drop dead when one wins over the other. and they dont fork off, they adhere to the new protocol and keep going.