Rollerballs, then ballpoint (which some switch to the gel refill -9000), then fountain pens.
Customers don't always know what they are looking for though - so if they are looking for a gift for someone else they will tend to roam toward the side of safety which for many will be the ballpoint side.
Personally - I carry each in my purse and I write with each. Part of this has to do with what setting I am writing in. At work if I am in a hurry and going to be taking a lot of notes in a fast paced setting I will generally use either my roller or my ballpoint depending on how my hand is cramping. If I am just signing off on things, I use my fountain.
Linda