Re: zero has a more good story but it will bore u, but SAO is real entertaining, bother are in my top five but I like SAO a little more so I've to say watchBOTH but SAO 1st
I think SAO is worth watching it has a good story, Re:Zero is good too but not as good as SAO, Subaru is the worst anime protagonist I’ve seen so far, I just think he’s a bit lame.