In Old Archades (the slum part of town where you first met Jules) there is a salesman who sells Embroidered Tippet which gives you double XP. On the Phon Coast, you have a salesman who sells Firefly accessories which make the wearer have 0 XP. Give the ET to who you want to level and the Firefly to his two allies. Your best bet for leveling will probably be either the Phon Coast or more likely the Tchitia Uplands and Cerobi Steepe (Use a chocobo to get here faster) there are some pretty good items in both areas and you'll get quick access to Balfoheim which is a beautiful port city that features some of the games better items. Once you gain some levels, go to Nabrudis to get some levels as well.

Yes, you get better XP and gil from Hunts, you may want to catch up on some of them. Also, you could try to acquire some of the espers as well. Adrammelch is probably useless to you now but, Cuchulain and Exodus should still be useful.