I'm totally against monthly limits, it doesn't solve the problem at all. The problem is available bandwidth at peak times, caps do nothing to curb usage during peak times.
It really is a toss up between options 2 and 3; both allow users to use their connection at full speed at peak time (providing sufficient network capacity) for at least a while. The benefit of option 3 is that it would only apply if the network was busy, otherwise everything is max speed
