Leslie, Kaverra, Riva, Julia, Sara the Fox, Alyssa, Adjona, and Boadice.
The ones you can hire without conflicts with any other female companions are imo the best among them:
Leslie - Essentially a female Ansen with slightly different starting skills. Can easily fill in for support.
Kaverra - A bit overlooked, but she does make a nice addition to the back of a shield wall with her Manopener and some throwing weapons.
Boadice - Strongest female companion, and starts off at a higher level than most companions.
Edit: Forgot to put Adjona here. Starts off with power draw, riding, and slightly higher looting skill than other companions.
That leaves you with the other 4. Each of them will conflict with a companion above or below them in this order.
Alyssa - A weaker snake priestess, but more potential than having an actual non-levelling snake priestess in your party.
Sara the Fox - Fast but fragile, and I think starts off with the highest persuasion skill of everybody. Can fill the role of Emissary.
Julia - Crossbow user with some riding skill. Can be given a horse for mobility or a heavier crossbow for pure damage.
Riva - No definite role from the start, but has riding and power draw, so I usually make her a horse archer.
This means you can only have 2 of the 4 without the deserter trick. Possible combinations:
Alyssa & Julia
Alyssa & Riva
Sara & Riva