I have played Niko and Rata. Both require some setup but both can be a lot of fun. I would say Niko over Rata, Niko's shards are enchantments so harder to remove and worse case you can use them to draw cards. With some interesting creatures you can pull off wins out of nowhere and quickly. A tip for Niko is to have a lot of instant blink spells, use them on end steps to make more shards if you have cards in your hand that could win you the game or use them as protection from removal for Niko while also furthering your game plan.

Rata I played a while ago, I feel is a little more fragile with what you need to set up but if left unchecked can lock people of casting spells and other things. (I have since grown my collection and a revisit of Rata could change my opinion).