Blackthorn because of the following reasons.
Ice Path and the route below Blackthorn were good training areas.
Jynx is in Ice Path, so definitely catching her.
Clair's my favorite Johto Gym Leader, so I like to drop in and say hey baby to her sometimes, I especially like the interaction in 4th gen Johto, I'm all like hey baby and she's all like hey let's exchange numbers and I'm like of course babe, call me.
Since I don't watch Smackdown anymore, I should call her up sometime for a battle.
I also got a picture of me, Clair and my Dragonite.
I also like to hatch eggs here because it has that long stretch, that route where with the daycare is too busy, too much grass to run into stupid Rattatas, at night that stiupid pig battles you, when he should keeping his eye on the day care man in whom is freaken staring at Picknicker Gina.
So yeah definitely Blackthorn.