they're fine.. the 840 evo is the only problematic ssd. everything else works fine. no real advantage or disadvantage.
I use my SSD for torrents, because my harddrives spin down.. so.. I got the 850 pro for that reason, as I have a large amount of writes.. but overall, if you're not torrenting to the SSD, it doesn't make a difference in terms of slc/mlc/tlc
vnand just means verticle stacking of the TLC used in the more budget friendly Evo series.
The Pro series uses MLC, which doubles the area of nand required to produce the same capacity, which is why it's more durable.