>>53861683Both very good in their own right.
I think Platinum might actually be the best pokemon game in terms of handling difficulty. Its not UBER HARD or anything but some of the gym leaders can be decently difficult for the point in the game you're at (gyms 6-8 start getting a little too easy though), the E4 and Champion are fair, and Cyrus in his final fight is no pushover either.
I like it a lot. There's more difficult fights in other games, but thats always in shit like USUM with Necrozma or BDSP's "competitive" elite 4 that randomly amp up the difficulty in an otherwise laughably easy game, so it feels unearned. I much prefer how Platinum handles it. I replayed Gens 3 & 4 recently (excluding RS and DP) and Platinum was probably the most challenging.
I like HGSS more in terms of aesthetic and the general vibe of the region. Some nice challenges postgame too. Both Platinum and HGSS are great.