Market Health is one of the best affiliate network i ever promoted. They pay commissions through paypal for every 15 days in time. I never had problem for the past two years with them. They have both flat CPA offers and 50% commission based on sales you make. You can choose the best option according to your campaign.

This is a screen shot taken from my account. Market Health affiliate network has plenty of health products to promote. Honestly i never had a single refund for the past two years. I am really happy with these people.
I highly recommend to join Market Health today and make some serious cash. They provide additional 5% of commissions from their sub affiliates too.