I think one of the first things that will help is to know what your definition of "efficient" is - mileage, use of secondary fuel, etc.
The second question is what is your budget? If you're holding around $1500, then the propane system is your only option. If you've got enough cash to put into injectors and custom program, plus (probably) a new HPOP, then you've got lots of options.
I'm slowly working toward the injector option myself. I've got a custom PCM, and just put in an HT Turbo (will see how that works this weekend), so am getting closer. I'll probably do an HPOP later this year, and be ready for injectors after that.
Crazy use of either large amounts of diesel or propane can result in the opportunity to see your connecting rods.
For the longevity purposes, as well as ease of use, I would suggest going the route of injectors. As long as you're not going crazy with them, and your tune is right, that should give you plenty of daily driver power, with the least amount of long-term effort. It will surely be the most expensive option ($7-9k with turbo, injectors, tunes, and HPOP), but probably the most fun.
