The standard approach for dealing with hills is to start at the bottom and work your way up....
Your approach is going to vary with what you need to do after the hill. Hammering for one mile isn't a great idea if you have more than 100 to go. But if you don't have much else afterwards, why not? Standing might not be efficient, but it allows you to rest your spinning muscles for a bit and it's perfectly legit to do this frequently. As a matter of fact, cresting while standing isn't a bad idea since you'll want to spin on the other side.