Honestly, I feel like the best value online MBAs would be from
Non-Top schools. Here's my reasoning:
An online MBA is good for skill acquisition only, it doesn't offer the ancillary MBA experience benefits (read: networking). For this reason, it will be the ultimate "make of it what you will" kind of thing: you can acquire just as many hard skills from a lower-ranked program as from a higher-ranked one if you just put in the effort.
Therefore, you should shop online MBAs primarily on price. At a prestigious school's web-based MBA, you'll likely pay more, but not for a better education. You'll be paying exclusively for the name, without the networking access that usually comes with that name. Sure, you'll be put in a cohort of people you'll know through the internet, and sure you'll have access to the school's career services office and alum community, but nothing will replace the peer-group bonding, intellectual cross-pollinating, etc that happens in an on campus program.
As for the signalling function of a prestigious school on your resume ("wow, this candidate went to X, he must be more competent than others"), I think it is too early in the Online MBA era to tell how they are regarded by hiring committees. Is the signal discounted by not being full-time?
How much of an asterisk does it put next to the fancy name? University of Phoenix is the first name in online degrees, and the first thing most people think of in online education, so I wonder if they aren't tarnishing the whole category.
Basically, a lower-ranked program can offer you everything a higher-ranked program can online, and that which a higher-ranked program offers that a lower-ranked program doesn't can't be gotten online anyway.