If you just want to protect against pedal gouges then I would say some sort of thin soccer shin guard would be the best. If you want to protect against real impacts then you need something a bit more robust that will stay in place when you fall. Also, protecting your knees in a fall is more important than your shins. The shins can take a beating and heal up well, knees can be permanently messed up. I only wear protection if I am practicing tricky techniques that involve speed. I use THE storm shin and knee protectors, which work pretty well (stay in place during riding/falling, and decent ventilation). The main drawback is that the upper thigh strap was too short, and I had to take it to a seamstress to get it extended a bit.
I've found for me the best shin protection has been having good, grippy pedals and shoes. The only times I have slipped a pedal for awhile has been when my shoes were covered in ice/snow/mud, and I forgot to knock some off.