64 pitch is a little harder to set mesh (for beginners), and may lack some durability compared to 48. But, offers a lot more adjustability with gear ratios. One tooth on 64 is very subtle, one tooth with 48 is more drastic. Stick to 48 if you are a beginner, then switch later on as skills increase. Plus depends a lot on which type of racing you do. Offroad, more stress and debris, so 48, onroad or oval 64 will be better.
"They may be toy cars, but I spend REAL money to race them!"- Racer X
"It's only a big deal if you make it one."