I have a Reshiram, a Zekrom and a Kyurem. I want them all but I heard that I can fuse one of the other Pokemon with Kyurem, but I'm a little worried that if I fuse it with Reshiram it will disappear, and vice versa. If I do fuse which one is better?
However, you can unfuse Kyruem and your legendary when there is an open space in your party, meaning that your legendary will not disappear forever.
Reshiram will not disappear, you can un-fuse them by using the Splicers again.
They are quite hard to choose between, but I reccomend White-Kyrum.
Hope I Helped
Reshiram will not disappear.
You can simply undo the process by using the DNA Splicers. Just select White Kyurem with it and it will undo the process. By the way, which one is better is entirely up to you because this is opinion based.