Your only real choices are the entry-level Power Grooves, Scouts, Tropicals. At that point, one's just as good as another, though I believe the Reactor cover on the Tropicals is stronger than the PK17 on the Grooves. Let him pick the colors (and scents) he likes best, there really isn't much else to differentiate them. They're high-RG, lower-diff polished pearls with puck-style cores. Matching up is not exactly critical at that point.
SH