You are asking a series of questions that are difficult to answer without telling us how you want to use the machine. In my opinion all three options you list are well proven, safe and reliable as long as properly installed and maintained.
- Only mags stand any chance of surviving a lightning strike. They are also easily repaired in remote locations (when you don't live in the US this can be a consideration).
- The Lightspeed is redundant when installed on both sides, but relies on ship's power. Klaus has certified a version of it on the Cabri G2 helicopter (EASA) - supplemented by a mag on the other side. They need to be installed properly, locating coils in the wrong place and exposing the box to excessive vibration/heat has caused issues for some builders.
- P-mags will run on their own, without ship's power and are fully redundant. They are self contained and easy to install.
- EFII is a little cheaper than the others, but not redundant without the duel ECU option. Adding two ECUs and their electrical box significantly increases the complexity (and cost).
Performance and economy wise the electronic ignitions are the better option. They start more easily, produce more power and use less fuel. There is no free lunch - your engine may well get hotter due to the advance and need more cooling.
I don't think there has been a conclusive bake off of all of them, so no one can really tell you which system produces the most power. I really doubt there is a lot of difference between the electronic options.
On a four cylinder I'd buy duel P-Mags (and that is what I have been running for the last 500 hours). I like the ease of installation and redundancy. They have been bullet proof and the company support is outstanding if you need them.
If you really want performance, make sure you install a constant speed prop. That will make a lot more difference than a few extra HP from electronic ignition.