I'd say HGSS for sure. RFLG are good but they don't add much more. The point is that it was their first remake, so it makes sense to be very similar to the original games. Unfortunately, playing the first games is an experience of its own, simply because they're the first ones.
ORAS on the other hand chose a path that I really appreciated, which was to innovate things, making the remake a slightly different experience especially from Emerald, not ignoring the things it added to RS.
BDSP has a horrible artstyle and the friendship bonuses are a weird mechanic. I'm glad they improved AI and such, but it was too faithful. They remived HMs, which while it's something many people like, I think it was a necessary thing to keep in BDSP for a layer of difficulty (not much though tbh), to maintain the original feeling of the game and to allow nee players to find out the HM mechanic.The thing about older remakes was to add the new Pokemon to an older game, but this didn't happen in BDSP. Obviously, the Platinum part is totally missing, creating this weird situation for which a 2009 game can offer more than a 2021 game.
I don't really mind the way of faithful remakes, especially now that many games came out and younger generations might have problems in retriving the older ones, but I wouldn't go with that artstyle. I'd prefer a remastered version.