Paddle holsters allow you to carry without need for a belt. They are also great for adjusting forward or back when you get in and out of the car. I usually slip mine off and tuck it between the seats by my right leg when driving long distance.
Grip length and width seem to be the greatest obstacle to concealing. Single stack short grips disappear, Glock 17s are much more difficult depending on your size.
Ankle holsters are next to impossible to draw quickly under stress from.

Kramer Gun Leather makes a great paddle holster for ladies - depending on their shape. They also have other holsters designed for ladies, as do other companies.

Whatever you settle on, carry regularly and you will forget it's even there.