I had never played a Monster Hunter game or Dark Souls game before MHW, and I started with the Longsword without any issues. I didn’t like how mashy the dual blades seemed, and the S&S felt too slow.
Longsword has a lot of maneuverability, so I feel like it made the battles easier to learn, as you can just dance around the monster a bit to learn the moves, and then find openings for combos. I think that LS is very newbie friendly.
But also, remember, that the LS will interrupt combos of other players, so don’t be an idiot during teamfights. The LS person’s job is to cut off tails and other body parts, because they have the reach and slashing damage.