I have taken courses from both organisations. I think they complement each other quite well. there are however a few differences:
: If you go the ondemand route then you have access to a virtual mentor for a period of 4 months. They will answer just about ANY question you throw at them. And the turnaround times are usually quick. In my experience the VM[Virtual Mentors] have been quite knowledgeable.OFFSEC
: You are essentially on your own. In most instances you have to reach out to other students for assistance. It gets frustrating at times especially when your back is against the wall and you are told to "Try Harder".
: The material is solid although I have found a few instances where the material was incorrect or riddled with typos. They also seem to cover a broader range topics. So for instance the GPEN took the student through the entire sequence of events to perform a pentest - get out of jail free card, scoping, laws, rules of engagement and a host of other soft topics. OFFSEC
: Here again, the material is very good. It does however tend to be a bit more focused.
: Hands down the best lab I have experienced to date. And this is both in terms of layout and exercises.
: You actually recieve text books that you can add to your library I guess. The content is well laid out and easy to get through.OFFSEC
: You receieve a water marked pdf file. So in the end it boils down to preference. A pdf you can always take with you. Walking around with a bag full of books ................
: Still multiple choice. Now even though this is open book, if you do not KNOW the material you will still have a hard time passing.OFFSEC
:To the DEATH. Enough said
: Has a wider array of certifications to choose from. However OFFSEC has recently added a few new ones.
In the end it boils down to your learning style. If you want guidance and a bit of hand holding then go SANS. If you want to suffer immense pain then go OSCP. For best results do them both.