BDSP was a terrible remake that was farmed out to a random porting studio. It’s one of the lowest effort remakes I have ever experienced.

One of the biggest issues is BDSP added modern EXP share where all your pokemon gain EXP every battle.This caused a huge problem for BDSP because they didn’t re-balance the game to account for you gaining much more XP than the original developers expected. The game is completely trivial because you become unreasonably over-leveled when playing through the game normally.

Platinum also added extra content to gen 4 beyond the original Diamond and Perl. None of this content was added to the remaster. If you are wanting to play gen IV and have hardware that can run it, Platinum is the best choice.

Platinum came out a year after Diamond and Pearl, it made a lot of changes to the games. From the top of my head these are the most important ones:

• Expanded Pokedex from 151 to 210 or so pokemon.
• Revamped team galactic, changes their bases’ looks and adding tons of dialogue.
• Gym leaders, galatic leaders and elite four have improved teams due to the added pokemon.
• Improved sprites although this doesn’t really matter at this point.
• Added trainers that follow you and turn areas into pure double battles for a while.
• Improved the big showdown with team galatic and gave Giratina a role in the story.

BDSP are 1:1 Unity remakes of diamond and pearl, for better or worse. Platinum just had some small quality of life upgrades and both the legendaries.

Also, BDSP aren’t made by Pokemon Company, I enjoyed the games but artistically it’s just not Pokemon. If you told me BDSP was a fan game, I’d believe you. It’s cool to see a 3d chibi take of Pokemon but I love the art direction of the DS games far more.