Basically, the Private Pilot certificate is going to give you the most bang for your buck.

The Private Pilot certificate allows you to carry more passengers, gives you more freedom to fly anywhere you'd like, and allows you to split the cost of the flights.

The Recreation Pilot certificate limits you to just one passenger, restricts you to where and how far away from your departure you can fly.

The Sport Pilot restricts you to the gross weight of the aircraft, and the limits of where you can fly.