I'm basically completely unqualified to answer this question, so... Of course I'm going to give you my two cents.
I haven't really played any DS or GBA games. I was never a handheld gamer until the PSP, and I didn't actually get into it until the PSVita. I grabbed a handful of PSP games from GameStop before they stopped carrying them, so I have stuff like Crimson Gem Saga. I just haven't played it.
That said, I want to mention the
one PSP game that I played and really loved;
Queen's Blade Spiral Chaos. It's a tactical RPG, so don't expect classical RPG gameplay. It's based on the visual combat book game, which itself also has an anime series. Game-play-wise I hear it's a lot like the Super Robot Wars games. It also has an armor-break mechanic, which ties in to the pretty-girls-losing-clothing aspect of the original combat books. It's also in Japanese, so that's one consideration. I enjoyed it so much however, that I made a series of maybe 5-6 videos (
https://youtu.be/kEV9A0Z92EQ) about how to play, what all the menus say, and even strategy for a particular battle that's challenging early on in the game.
With the tips videos, and a FAQ on GameFAQs, I think anyone willing to take a stab at the game can play it just fine. I thought it was a lot of fun for what it's worth. I can't really recommend anything else though since that's basically the only RPG-ish game I've played on any of those handhelds.