Tell them the truth next time they want to know if they are "the best you ever had". I told me wife she wasn't crazy enough to ever be the best, but she was pretty good for a sane chick.
Drives 'em nuts. They just can't leave it alone and will constantly badger you with questions on "what made her so good in bed". After all, she does all the same things the PBFH did, what is the difference? Since it can't really be explained, nor do they ever have the slightest hope of ever competing at that level, it just eats at them.