The most important thing is that it is the right shape and size, so it will be comfortable, and he will actually wear it! Look for something with a lot of vents.
The Tipperary Sportage is great, lots of vents, lightweight, comfy. I had the old style and loved it. The new style isn't the right shape for my head, so it wasn't comfortable. I got the Ovation Protégé, which looks a lot like the Tipperary, and it is working well for me. It is also about $20 less expensive, and has the adjustable fit dial.