Originally Posted by
HillRider
Also, don't overbuy bearing grade. Grade 25 balls are the most commonly used and are far more than good enough but low enough in price to splurge on. Paying a huge premium for Grade 10 or for ceramic balls is a waste of money for no benefit.
Not really true though the quality of the hubs can have an impact as well. Dura Ace and Record come with higher grade bearings because they spin better and can last longer. Although I think ceramic often costs stupid amounts of money spending a little extra on hubs will help them spin a little better.
OP: Get the park spoke ruler for future such repairs, it has holes for all the sizes of bearings bikes use, which ever hole it barely manages to drop through is the size. When it doubt bring one of each to the LBS and they'll do just that or a good mechanic will just know by sight in all likelihood. Nothing wrong with changing them every few years, even if everything looks good bearings can deform from the pressures on them over time and new bearings will keep everything running smooth.