Which school, if any, would be best for applying to a top 20 grad school?

[davewill]

I can't really see enough difference between any of the Big3 or WGU to think that one over another would be "better" for getting into a top program. I think it would be best to think of your application as a whole, and ask yourself what kinds of internships and research opportunities you could take advantage of to boost your creds. Also, if you can wait a few years to get solid professional experience, that would help as well.

Another thing to look with grad programs is what prerequisites they require and whether they will accept those coming from alternative credit. Even if they do, you may want to take those courses from an actual university and not have to deal with the question of where they came from. That also has the advantage of giving you a GPA that has some meaning, since alternative credit doesn't generate grades.

As far as transferring to some other school to finish your undergrad, there's no way to "legitimize" alternative credit. This is something we call "credit laundering" around here, and it comes up regularly. Each school evaluates credit on it's own merits, not on whether another school accepted it. If you want to use alternative credit for your undergrad, you must get your degree from a school that will accept it. Putting it on another school's transcript first won't help.