What kinds of dairy/cheese have the most/least amounts of lactose?

I know there are certain kinds of dairy that have less lactose than others (i.e. yogurt doesn't seem to affect me, but some hard cheeses do). Also, does fat content make a difference in terms of lactose? Does low-fat milk have less lactose than 2% or whole milk? And should I avoid condensed milk altogether? I am not severely lactose intolerant, but some types of dairy to seem to upset my stomach or give me gas. I love dairy too much to give it up entirely, but I am hoping someone out there has more info about which types of dairy I should most try to avoid.