SVE adds so much to the vanilla game that you could consider it an unofficial expansion rather than just a mod. I might say try vanilla first if canon is important to you and you want to experience the story without any non-official changes.
If you don't care about any of that, definitely dive right into SVE. It has a personality all its own that blends nicely with the vanilla game. It adds tons of stuff (characters, new areas, events, etc) and takes a lot of creative liberties to flesh out the world and lore.