I'm a recent convert to the Shadow from Swell Catamarans - a high performance singlehander, with spinnaker. It's light (99Kg) and well put together. As the baby sister to the Spitfire, it is a dedicated singlehander, although it has room for a passenger. There's no jib and only one trapeze, so the 'passenger' option is for recreation only.

As ever, you will need to decide what sort of sailing you will do. If you are competing, go with the crowd, if it is liesure on a budget, maybe the H16 or smaller, and if you're competitive with the occasional crew, an F16 looks like a good design. However, being "competitive with the occasional crew" may be more difficult than you think - you both need to know what you're doing, especially on the smaller boats with a kite.

Take a look round the forum - there's loads of advice along these lines.