I have one friend who ONLY comes to my house. In 3 years (since I moved out of the road where she still lives), I have only been to her house twice. She comes every week (without fail), unless I or she happens to be on holiday. She is very reliable, every week, on the dot, she turns up but she cannot take the hint that may be I would like to go to her house for a change.
I have another (ex?) (girl) friend who blows hot and cold all the time. She will phone up, we will make "definite" arrangements and then, at the last minute, cancel. When this happens more often than not, I have decided she is no longer a "reliable" friend and I have made new friends from my son's nursery who are more reliable/consistent in their friendship.
I also have some friends of long-standing (one of 20 years and one of about 17 years) and neither of them live close to me. We only chat once every few weeks and see each other two or three times a year, but I know they would always be there for me (as I would be for them). Even though we don't see each other that often, they are still good friends and very reliable.
I do find with some friends that you have an "equal" relationship but with others, the relationship is always one sided, i.e. they just take, take, take.
I can count on one hand my friends that I know I could truly count on. As was mentioned earlier, I definitely agree quality is more important than quantity.