ThinkComputers tries to settle the debate on multi rail vs single rail power supplies, you can read their editorial over here. The conclusion is that the number of rails in a power supply doesn't matter and shouldn't be a deciding factor when making a purchase.
Ever since multi-rail PSUs were introduced, we’ve seen enthusiasts adamantly claim that one or the other PSU type is better. Some claim single rail is better for overclocking. Some claim multi-rail is safer. Single rail is cleaner. Multi-rail more efficient. The list goes on and on, so who’s right? People on either side argue their points and pick up uninformed followers along the way, resulting in the same rehashed marketing over and over again from companies playing on this vehement fanboyism: A single strong 12v rail! Multi-rail for extra stability! Blah blah. Which is better? How does this apply to me?