Its always been Nintendo plus... for me. Because Nintendo has Zelda. That plus depends on which other system has the best games.
This has changed a couple times throughout the generations. It has been PlayStation in the 5th, 7th and 8th gen, and its extremely likely that it will again be PlayStation in the 9th gen because I dont think its plausible that Microsoft will all of a sudden have a whole bunch of exclusives beter than PlayStation. One might say get both (or; all, if theres going to be more), but at some point the libraries are so similar there is no point in getting both, and I could live without the one or two good exclusives the other has.