A few more points to consider since myth's setting is maybe a bit different than what people are used to, I won't give you outside knowledge but this information is all based on assumptions/knowledge your character would make or has so it should be fine to tell you:
The Imperials:
These are the guys with the good stuff, armoured soldiers, archers with fire arrows, maybe even the odd Heron Guard if you play your cards right.
Now the Heron Guards are a mix of a Paladin and a Samurai and one of them is easily worth ten soldiers according to the fluff so they have their uses but they are utterly loyal to the Emperor and the empire.
The Thieves Guilds:
These vary in quality and type. Some are honourable, some are not, some have a large number of former fighters/sell-swords, some rely more on agile/stealthy types. You don't know what kind of guild Brigit belongs to though if she is typical of her guild it will be the stealthy/agile/silent kind. But they could also lend you a few enforcers if you make a good impression/help them out.
The Tent Camp:
As already mentioned you do not know what you will find, neither do I in fact. Oddly enough this is sort of the quality over quantity option given how all of the backgrounds were people of exceptional character.
You may find a skilled officer, a down on his luck inventor or a medic, or you might wind up with the Courtesan. Not sure how useful she would be in a dungeon crawl, maybe you could swap spells... and other things...
The Mercenaries:
This is the muscle option, the meat shields, maybe with some archer support. They tend to organize in 10 men teams from what you have seen. This is a quantity over quality option, if you get them killed well you don't have to pay them I guess.
On the mage circles:
These are organizations formed fundamentally out of self interest, a successful mage is never really going to trust another mage so if you go to the circles you will be trying to enlist the help of a single mage or maybe two potentially along with any apprentices or bodyguards they may have. Warlocks are damage oriented spellcasters, these are your fireball guys, mobile artillery so to speak. The Children (as mentioned by Esquilax) are my own creation, they are a "kinder, gentler" version of the Warlocks with a taste for knowledge and proficiency in manipulation and illusion (oh, they are still mages remember and everything I said about the Warlocks may apply as well, guess you will just have to try them to find out)