The first thing you need to look at (if you want to race) is what boats are in the fleet you would be sailing with then look into which of those would be a good fit for you. Get rides, tips, info, etc.

That said, I would agree with the advice to get an H16. I feel they are the biggest bang for you buck when you buy used. As a general statement in the US an H16 will almost always allow you racing opportunities.

Here are my reasons for picking the H16 as a starter boat for those interested in racing or not:

1) They are cheap used. About $1000 - $2000 depending on condition, extras, trailer, and location.
2) They are very easy to sail solo and with crew.
3) Parts availability. They are still in production and there are thousands of used ones out there too.
4) They are relatively simple boats to rig and derig.
5) There is a huge base of people all over that know the boat and can help you with tuning, repairs, and sailing tips.
6) The boat will be able to challenge you as a newbie and as a more experience sailor.
7) They can take a beating and hold up very well. Yes, they hvae thier issues, but what boat doesn't.
8) You can double trap on an H16 and not on a Wave.

Those are all of the major points I can think of right now.

Again, talk to those in the area who you will be sailing with and get rides on a model you are thinking of buying before you make up your mind.

My 2 cents...