Flyboy, the raceboard will by far be the best for learning, and will also be an awesome ultimate marginal wind board later, maybe impossible to beat even for advanced riders.
Your first attempts will always be pathetic - it is very very normal for everyone, no matter what - dont be discouraged by that.
I would learn to ride on that one - it has tracks now and is way easier to learn on than the smaller ones.
For an allround board for ALL conditions, the Slingshot board looks just perfect in every way, and would also be easy to learn on and can ride in quite low winds too
But as it has not got tracks, but the raceboard has - learn on that one for now
The red one will be the most difficult - fine and small and fun WHEN you have learned, but will only be after a long time you will enjoy that one, short and tiny nose and no scoop, not good till you can foil consistently
PS: To Thomas1kite, for racing these boards are too wide, and will catch when edged max and really powered....
But for learning and marginal wind, top !