I don’t really get the rouge suggestion. Obviously, you can pick anything and it will probably be fine, but why single rouges out?
1) Expertise helps a new player who may not have the best stats.
2) It's simple. You just hit things that are standing next to an ally. You don't need to know about spells, spell slot usage, managing rests for spell slots. You just hit things. Generally, I err away from suggesting any casters for new players specifically because of lack of knowledge of spells will be significant. Having to learn the games systems is a task in of itself, without having to be overwhelmed by the many spell choices.
3) Cunning Actions are very useful. They provide a lot of flexibility which is useful for a new player who might not position optimally and thus rely of Dash/Disengage more often.
4) They're generally easy going on stats. You max out Dex, splash some Con and... That's it. Everything else is gravy. Which given a new player is more likely to use suggested stats (Which doesn't min/max) you'll be pretty comfortable with your effectivness.
5) "You already have Astarion available" I generally don't assume that every new player ends up having every companion with them. It's plenty possible to not get Astarion or to simply kill him at one of the several opportunities to do so.
