It depends on what you need so to speak.... they all get the job done but all have diff price points:
Magoosh - $99
eGMAT - now that they have both Q and V; it is $199 for Verbal + Quant. Probably one of the most comprehensive courses, esp if you get the online one. I don't know much about Quant though as it has just launched.
GMAT Pill is intensive prep and is designed to be covered in a few weeks, rather than months.
Optimus Prep - i have heard good things about their course but I have not seen it yet
I would review all of their money back policies and find the one that sounds and seems the best to you.