A company can pay for the number of servers it uses through additional maintenance and service fees. Yes, this is definitely a pricing model that melds nicely with the Internet. So, free e-learning is a natural extension of these Internet times. Some of its clients are Dell Computer and Barnes and Noble. Payment based on time.
Some pricing is based on the time spent in a learning session.
That's akin to asking what's the best car on the market. Similarly, I can't tell you what the best pricing model is for your organization. You'll need to identify clearly what you're trying to accomplish with your e-learning strategy, business requirements, and operational environment to answer that question. All of the pricing models have strengths and weaknesses. So, you make the decision that will support your goals best.