Another vote for Dynaplug. Two reasons for my recommendation; first experience tells me it works and secondly, and importantly, it is the only system I've seen that is made of metal. My experience of this is limited to the kits stocked by my LBS. The amount of force needed to either make a hole larger to fit the plug or to push the plug in can be considerable. I would worry one made of plastic could snap.
My kit comes with both large and small plugs. I've only used the small ones to date. You can consider a plug a permanent repair.
A plug kit is an essential tool on the road. It will take 5 - 10 minutes at most to plug a puncture.