Sex scenes can be plot/character relevant, if done correctly.
Okay, this is going to start off really bizarre because I'm referencing an eroge made by a conglomeration of 4channers with a deliberately offensive title and somewhat uncomfortable inspiration that I still can't quite believe I actually played.
HOWEVER. In the game Katawa Shoujo, there are generally 1-2 sex scenes per route (chosen love interest determines route) and they are made to be plot/character relevant--one girl has 2 scenes, and the first is primarily to show how desperately she's trying to break herself down. Her second scene is after she's gotten some help, and it's to sort of show off that new lightness of character. Another girl has only one scene, and it's only because she's got something to prove and nearly leads to your break-up. Another girl's scene shows a somewhat hidden side of her personality, and you also almost die because you have a heart condition and haven't been taking your meds. Another is wicked awkward only because y'all have no idea what you're doing. The only real super funtimes scene in the game is with the only girl on whose route you aren't drowning in each other and it's treated as the culmination of a healthy relationship as you both are about to graduate and go your separate ways.
I will say the art in almost all cases was overly graphic and would definitely be better handled in a #3-style method, so.
But it is possible to have sex scenes that don't skip on character developement.
Another HOWEVER: There has been a discussion of a 'sexuality flag' placed in the character creator, and I would actually like to see that. But not in the way straight dudebros seem to want. Your sexuality has nothing to do with what people hit on you/think you're hot, but it does affect whether or not you have sex. So I would like an asexuality flag, so the standard sex scene for each LI is replaced with a short conversation where similar character developement/soul-baring takes place.
But yeah overall my vote is optional #3 with less fear of female nipples as well so we don't go from 'awkward underwear' to 'what even is this camera angle did caravaggio light this scene' sort of thing.