I love both Dawn of Sorrow and Portrait of Ruin, I couldn't pick a favorite. I had fun capturing all the souls in Dawn of Sorrow and upgrading weapons. Portrait of Ruin has a bunch of little quests which makes it feel like even more of a RPG. A big difference is that you control one character in DoS and two characters in PoR. You might find it easier to play DoS first so you can learn all the controls/commands while dealing with only one guy. (But I played PoR first so the order is not all that important.)

I don't think you'll be disappointed in either one, but they'd be super easy to trade for something else if you decide Castlevania is not your cuppa tea. If you're in the US, make sure you don't pay more than $20 for DoS -- Konami has re-released it at a new lower price. I was thankful for that because until then all the shops in town were charging $30 for it used.

I've never played Pokemon, but I am currently playing Phoenix Wright: Ace Attorney and I think you should save up for Pokemon. Phoenix Wright is good (not great) and funny in parts, but it's really a whole lot of reading text and hitting the A button so you can read even more text. During cross-examination you basically press the witness on everything they say and present evidence when you spot a contradiction. It's kinda boring, rather easy, and I'm glad I only paid $16 for it at Circuit City. Even if I really loved it (like so many people seem to!), I doubt I'd play through it again.