Salamence97, this thread is not a RMT thread. You just need to wait until someone responds to your RMT in the RMT forum. This thread is for questions about the Ubers metagame.
For you question, it depends on what you need. Zekrom can setup on Ferrothorn, but it doesn't seem like you have a problem with it, whereas Darkrai's combination of Dark Void + Substitute can be often frustrating, as many users rely on their Choice Scarf users to revenge Darkrai, and Substitute makes this almost impossible. I suppose the best you could do is simply try each one, and decide for yourself what suits your team best.