Dawn of Sorrow: IMO, the best in terms of gameplay. The Soul System is awesome, giving a ton to collect and in terms of customisation. It is rather short, and feels kinda dated when compared to the other two, but still, the best in the lot, IMO. And the extra modes are the best. Come on, a mini-SotN is made of pure win
Portrait of Ruin: If I had to choose between PoR and DoS, DoS would win by the SLIMMEST margin. I love PoR. It has the best features (amount of items, dual-character system, magic and weapons, etc.), but it suffers from a repetitive map configuration. The use of the same map layout for the second part of the game is the main flaw of this game. The extra modes are "meh", at best, to be honest.
Order of Ecclesia: I don't understand why everyone loves this game so much. I couldn't advance in the story a lot, just because I couldn't bare the terrible gameplay. Yes, I think it's terrible. They Glyph System is awful -- it has you CONSTANTLY switching sets to do SOME damage on the enemies. The game is hard all by itself, we don't need an added nuisance like that one, thank you. Besides, is there any logic behind the Glyph System? Are you using the same "mystic force" that powers the Glyphs to swing a sword and to cast an elemental spell? Wow. Like Rayder said, I find the game to be too hard and frustrating to be of any fun.