If you play in CO and have to buy just one, I recommend the Molten BV5000. How's that for simple?  If you want more info, here's the reasons:

 

First of all it's important to understand that outdoor balls play very differently than indoor balls. If you want to make the transition from indoor to outdoor, you're gonna have to change how you play the game, and the ball you play it with.  When it comes to outdoor volleyballs, the choice is really between 3 options.  The Wilson Official AVP Volleyball, the Spalding King of the Beach Volleyball, or the Molten BV5000.  The biggest deciding factor in my recommendation is that most divisions you'll play in for CO tournaments will play with the Molten.  The rest of the differences are pretty minor and you'll get used to any ball you play with.  Until 2015, most CO tournaments played with the Spalding.  We will continue to sell both the Spalding and the Molten until demand for the Spalding disappears.

 

The differences: 

 

-The feel is different.  The Spalding has more pronouced ridges (although less than they used to be).

-They serve differently.  For a float serve I prefer the Molten.  It has more movement, and the distance seems more controllable than  

         the Spalding (especially when they're brand new), but the Spalding is preferred for top spin serves. 

-They pass differently.  The Molten is generally more controllable and predictable ball to ball.

-They hit differently.  Overall the Spalding is a faster ball all the way around.

-Most CO tournament divisions play with the Molten.

-Cost:  The from manufacturer cost is higher for the Molten, however they retail for a similar $40-$45.

 

Everybody is going to have a slight preference, but if you're going to play a lot, you'd better be able to play with any ball, but if you're playing that much you probably already have your own opinions and don't need this guide:)