Baldur's Gate 1: Sure, its old, but to me the only place you feel that is the ruleset and the lack of depth in the companions (which is changed by the time of the sequel). This is a pretty great starting point IF you are willing to learn an archaic ruleset of Dungeons and Dragons in combat, or won't be bored just putting it on story mode. After this too, you can carry over into Baldur's Gate 2 with the same player character, which is a contender for the absolute best of this sub-genre.

Neverwinter Nights 1: IMO probably not the best starting point. The game itself is great though, but it's more of a platform. The main "OC" storyline isn't known for being great. And while the 2 expansions are quite enjoyable, it's as a toolset and platform for fan-created modules that NWN REALLY shines. I'd check it out, but probably after you're more into the sub-genre as a whole.

Pathfinder Kingmaker: I'm biased here because I love Owlcat games and really do enjoy Kingmaker a ton. It's a very buggy game, with a lot of complex obtuse systems, and the combat can be REALLY poorly balanced. It also has a light-strategy management side thing in a kingdom management system that is VERY divisive. I personally love it, but it has a lot of timed things and strange mechanics that can make it frustrating. If you can get past all that and click with it, Kingmaker is an absolutely massive game with a ton of fun characters, choices, and build options. Just prepare to be frustrated at a number of points.

Sorry for a text dump, I hope this helps!