I prefer more solid goals, like Top Coordinator - win a Grand Festival to more vague goals, eg. Water Master / Dragon Master. I know it has been specified that Dragon Master = understanding a dragon, but there's no like, tests or anything to show that you truly understand dragons. I mean, I can just go pick up a frowny Deino and say it's hungry. Or a happy Dratini and say, it really likes its trainer! There's no solid tests / competitions or anything, but I have to agree that Dragon Master goals are much more defined than Misty's Water Master Goal (Don't quote me on that).
Though, I don't really mind vague goals as long as it is properly developed and isn't crammed into a tiny amount of time. I mean, take Iris. I feel that during BW Iris is just liek lolololol i'm walking with this kibago in my hair on my way to bec0m3 a dr@g0n m@st3r with only one dragon type who gets lost a lot! Then BW2 came and it feels really... crammed I guess. She gets Dragonite, her first strong dragon. Kibago gets development vs Cynthia's Garchomp. Dragonite beats two ice type. Iris's Dragon Master goal is reexplored vs Shaga. To me, I think that Iris could've caught a 'psuedo-Dragonite' during her stay in BW and evolve it during BW2. No offense to you all Iris-fans, but it feels to me that the writers are trying to cram Iris's Dragon Master Goal into a short period of time so when they write her off the show, she will have something to brag about. I no likez. That's why I prefer contests. It's progressive. 1 ribbon, 1 ribbon, 1 ribbon, 1 ribbon, 1 ribbon, Grand Festival!
Those are just my personal stances. Feel free to disagree ~