Hi Dave,
I have been involved in the sports betting side of affiliate business for a numnber of years, and tried out the casino, poker and bingo side and found the majority of money I see affiliates making and IO personally make derive from sports betting.
With sports betting you will see the player retention to be around 1.5 years, compared to the casino side being on average just a few months.
Getting a sports bettor is a little bit tougher than the casino side, but the gambler is worth five times the value of a casino gambler, so your effort pays off.
I recently launched http://www.gcmoney.com, and also a few years ago I launched http://www.vipprofits.com which are two extremely competitive affiliate programs worth looking at and signing up to see what it is all about.