I would set him loose on the Chicken Chart:
http://www.ithaca.edu/staff/jhenderson/chooks/chooks.html
It's a fabulous resource that gives you size, links to pictures, rarity, temperament, and other qualities. You can maintain a veto over any that have difficult temperaments or special needs, but he can spend a lot of time researching to find out what is important to him.
Is the 4H group ordering as a group? If so, they may already have a source in mind. You'll want to know what your breed choices are.
My daughter is younger, and in 4H. It is much more fun if the bird will be competitive at a show. If the club is just ordering from a random hatchery/feed store, it might be worth the effort to get him a chicken from better bred lines. It doesn't have to be the winner, but you don't want it last every time or DQed. If you're getting chicks, 5 is a good number to give you some to choose from.
When looking at breeds, keep in mind that some varieties are harder to show or get show quality individuals. Colors with a lot of variation, like speckled, will be harder; certain varieties in certain breeds may not tend to be on-type for that breed. Ameraucanas, for example, as lovely as they are, are not a good choice for a show bird unless you have access to a very good breeder. In other breeds, hatchery birds are more likely to be on type, especially in the simpler colors.
Old English Game are lovely birds, but the roosters have to be dubbed to show.
If you want a breed that is unusual for your area, ask the leader to see what is most typically shown. The most popular bantam breeds in our area tend to be the Silkies, Polish, Cochins, OEG, and D'uccles.