Symphony is probably my favourite. I'm not the biggest Castlevania fan or anything, but I have played a number of the Metroidvanias and really like some of the old school games too (III, IV, Bloodlines, etc). Dawn of Sorrow is probably my second favourite Metroidvania, although what drags it down is the random drop mechanics. I hate random drop farming, and Konami went and made it one of the core mechanics in the game. Ugh.

I also have a soft spot for Castlevania 64 (yes the one everyone hates). It's not at all a bad game, and it was genuinely creepy in parts. I still remember really digging that villa level and I wish another game in the series could do something like that. I also played Lords of Shadow not too long ago. I don't recommend it to anyone.

Sometimes I really, really wish there could be a great 3D Castlevania game on modern consoles and I wonder why Konami haven't been able to put it together. But then I realize that there are two absolutely amazing Castlevania games on the PS3: Demon's Souls and Dark Souls.

So,

Fave 2D entry: Symphony of the Night
Fave 3D entry: Dark Souls