The 3ds is my first portable, so I won´t speculate about Ds rpg´s
Some good games on 3ds are: Shin Megami Tensei IV, Etrian Odyssey IV, Fire Emblem (more strategy than rpg, actually), Mario & Luigi Dream Team, Paper Mario Sticker Star, Rune Factory 4, and (some people will bash me on this, but I do think it´s a good game) Heroes of Ruin