what do scientists believe may be the fate of the universe? which theory do you feel is the better explanation of what may happen? why?

Currently, there are four theories used by scientist to predict the world's fate. What we know for sure is that the sun's temperature increases by 6% every billion years, and according to the previous evolution of this result, it is estimated that the time left for this humanity is around 1.1 billion of years.

The Big Rip = This one establishes that the upcoming new form of energy, called "dark matter", is expanding increasinly over planets and galaxies in the universe. this theory establishes that, in a far future, all planets will not longer be able to hold this expansion and the gravity the keep them together will rip them apart. The Big Freeze = On this one it is said that the universe will continue expanding until all planets, stars and galaxies will end up keeping apart fom one another at a ery large distance. thus, they will not receive enough warmth and this warmth will disipate on the empy space. Therefore, once the temperature reaches zero, it won't be posible to have life here.The Big Crunch = As the opposite to the Big Bang, the big crunch establishes that the universe will not continue to expand forever. however, there will be a point where the universe will stop expanding and will start collapsing itself.The Big Slurp = this one has been released recently and it is focused on the Higgs Boson particle, saying that according to its weight it may be unstable and, at the moment of appearing another "bubble" from other universe in ours, it can be completely  annihilated.

Let me know if you have any questions :D

The answer is observations and interpreting.