How to choose a main character?

Question: My novel has two characters (both female)that are best friends, and out of all the characters I've created, they were the two I spent the most time on. At first, it was Character 1 that caught my attention. But as time went on, I went on to develop Character 2 and now I can't decide which to use with close third point of view.

I can't choose which one.
They're opposites, but not to the point where it seems like they have nothing in common.

I know an easy choice out is to alternate the two characters every chapter or so, but it just doesn't flow as well.

Also, I'm kind of worried about how the characters will appeal to the readers.
Character 1 is insightful, determined, seems to be "full of anger", unfailingly loyal, and somewhat reserved with a twisted past.

Character 2 is compassionate, loyal, vivacious, fiercely protective, and arrogant with the "comes from an aristocratic background, but cut off all ties" past.

How would I choose a main character out of the two? How to choose a main character?

Answer: Some things you might ask yourself...

1. If you know who your readers are, that might tell you which character they are more likely to empathize with.

2. Whose story is the most interesting? That is, who faces the most pressure to change over the course of the story? Who faces the deepest personal crisis? She may be your best main character.

3. It sounds like one of these two characters is the main character and the other is the impact character (the character who sets an example of what the main character could become, or pressures the main character to change). So which character has the biggest influence on the other? The influenser will likely be the best impact character and the influenced will be the best main character.

4. Is one of them the protagonist (i.e. the person most in pursuit of the resolution of the story problem)? Main characters are not always the protagonist, but they usually are.

5. If the main character is the protagonist, then her decision (whether or not to change) will determine the outcome of the story. However, even if the main character is not the protagonist, the resolution of her inner conflict will usually hold the key to solving the external problem.

6. Whose point of view is most interesting to write from? In third person, limited narration, you will be narrating the feelings and thoughts of the main character. So whoever's thoughts are more fun/appealing/charming may make a better main character.

Hope that helps with your decision.