Which qualities should I look for in a driveway sealer for new asphalt?
You're looking for two things: 1) wear surface, and 2) adhesion. 

1) Wear surface: There's always good-better-and best in all things. Asphalt coatings are no different. Asphalt coatings are a oil-based product and wear has to do with particles in the compound (liquid). When oil is "refined", it has chemicals and particles that can be used for asphalt coatings, roofing, etc. (How it's refined give you the good-better-and best results. I don't know how to determine which is best, but see item 2), below.)

2) Adhesion: Look for a coating with a "gel base", not a "latex base". Gels flow, coat and adhere better. (Btw, the warranty is longer with gels too. I think warranties are 3-5 years with latex and 7-8 years with gels.)

Btw, you said you have NEW asphalt. Do not coat or seal it until it's "cured"...about 6 months. Follow the directions...clean, apply at correct temperature, etc.