I wish Seven had a time attack and museum option on the main menu, and also a NG+ feature. I also wish Seven (and MoC) had Inferno Mode too, but I'd be satisfied with just the former three extras.
I like the gameplay of Seven better. Jumping is nice and adds the 3D aspect to the game, but I'll take dodging and flash guarding over it given the choice.
I like the OSTs about the same. Really solid tracks in both games.
I like Oath's plot better, but Seven's plot has a "grander" feel to it. Seven is definitely the bigger game, both in terms of size/number of locations and number of accessories/equipment courtesy of the crafting system, which Oath lacks. There's just more to do in Seven, even if we don't count the fact that Seven is like three times as long as Oath.
I liked the characters in Oath better, but this could be due to Oath having voice acting to give them more life. If I hadn't done my first Oath playthrough with voices on I might think differently, who knows.
Oath handled its epilogue better. It allowed you to control Adol so that you could go to all the townspeople yourself to say goodbye before you sail away. Seven just gives the typical epilogue where we're shown scenes of what happened in the aftermath of Adol's grand adventure.
Both have bittersweet endings in true Ys fashion. I thought it was stupid how they brought Tia with them only for her to burst into cherry blossom petals and fade out of existence. It felt like the writers had no idea how to kill her off so they just pulled a reason for her death out of their derrieres.
Despite most of these points favoring Oath in Felghana, I'm really not sure which I consider the better game. These two are the only Ys games that I can't make up my mind about. With all the other games, it's easy to compare two of them and say that one is better than the other. For some reason, it bothers me.
"Remember kid, there's heroes and there's legends. Heroes get remembered, but legends never die. Follow your heart kid, and you'll never go wrong."