Best way to level, while also maximizing stat growth for your characters is to pick an area which allows you to field as many units as possible and make them all the same class. Rinse and repeat until they're at 100 in all their base stats and all your generic classes are 50. For unique classes, you might want to level them solo or just field a few characters with these classes together and level them.
Put your low level units with good units who can clear the stage. Go to Tynmouth Hill or however it's spelt. Put everyone on AI. Browse intrawebs/watch netflix while they clear the stage. Start it up again and repeat as many times as necessary.
I play by my own rules. Nobody else's. Not even my own. Currently Playing: Tactics Ogre (PSP), Super Mario Galaxy 2
Divine Knights will be hard to level, you can try soloing tynemouth with them and that will rack the exp in.
In a typical tynemouth battle.. all the way up to level 50 almost. Bringing a full party of the same classes will net you a level every other battle with that class. You can do that with angel knight, but having the slots for 6 generics to be angel knight and making 6 of them is generally very difficult to do.
I'd try soloing the area, make sure your angel knight has awesome gear for its level, healing items and then destroy. Might be good as well, since you'll be able to pick up tarot cards just for that unit.
http://www.youtube.com/watch?v=jZM4NIVIOUI Tomorrow is the future.
I found that Phorampa wildwoods CH 1 maps are easiest to level in. Especially for classes that are really hard to get IE. lich and DK or unique classes like knight commander,paladin,astromancer ex.... All 4 of these maps can be beat by 2 to 3 leveled toons so feild 3 toons and your low level toon. When you beat it if your 3 leveled toons are all same level your low level should get about 600 xp per battle.
Jump to the part in ch4 right before you get the Lord/Princess marks, go to Phidoch, go back to Barnicia, go to Boulder Sands.
12 characters allowed, boss can be one-shotted with a good bow (and even if she can't you have an easy 2-3 turns of sniping before anything can hurt your characters anyway). Only problem is that you might lose out on one character to do the bow work when leveling classes without ranged weapons.
Going to 3L right before the Ozma battle with Hobyrim as a high-level guest can also work, but Ozma is hard to get before she runs out of range and Hobyrim won't usually target her right away even if he's an Archer. In theory that battle can allow you to level 13 people at once though (12 + Hobyrim himself).