Just to clarify, you want logical reads to be higher than physical reads (this is based on caching, if you're low on memory or its the first time in a while that you've hit that data it will not be cached) but you want to strive to keep BOTH numbers low. Really low! Obviously if you have a lot of data it can't always be helped. I typically pay extra attention to any operation generating more than 1500-2000 reads, just as my own baseline.
Andy