ABEC 9 is the highest. And don't waste your money. There are so many myths around bearings that its baffling to me. Let me explain.
The ABEC rating has to do with how smoothly the bearing will operate under certain conditions - and the ABEC standards are really meant to accomodate INDUSTRIAL MACHINERY. The ratings, from lowest to highest, are 1-3-5-7-9.
ABEC 1 bearings will get a maximum of 38,000 revolutions per minute. This is a ridiculous number that you'll NEVER get as a skater, if that's your purpose for asking. And those are ABEC 1 bearings!
To recive the benefit from the "smoothness" that higher ABEC ratings offer, you would have to have bearings shielded from all shock, something thats impossible for most conditions.
The higher ABEC ratings will NOT make you go faster and will give you no noticable benefits in terms of smoothness.
The poster specializes in inline hocky skate repair for a major hockey retailer.