Some Planeswalker advice please.
So I have been saving up crystals for Nahiri, I currently have 925. I have one of each dual color combinations asside from red/white and black/green currently with most at level 50, and all the original gatewatch, at 48. Should I start going for some of the mono Walkers, and if so which would be good to go for? Or should I just save crystals for packs at this point?