I just bought my lift today after researching and exploring my options for about a month. I bought a Poly Performance Stage III kit + extras.
When it comes to something as vital as suspension, I look at a complete package from an engineering standpoint. Everyone has nice kits, but I'm convinced that NO ONE has spent the engineering time that Poly has. Everything...from the high-steer instead of a drop pitman to maintain correct geometry and prevent bump steer, to including both front and rear track bar brackets that raise the roll center by 3" to maintain/improve vehicle handling, to the built-in SS relocation, to the on-vehicle control-arm adjustability using pinch bolts instead of relying on jam nut torque, to the rear shock mounting...EVERYTHING was thought through and designed as a cohesive unit to lift the vehicle CORRECTLY and address all the geometry and strength issues that occur when you lift. If there's a better-designed or more complete kit out there, I sure haven't seen it. It bolts on to boot. Was it expensive? Hell yeah, $3500 after the additions...but I have no doubt it'll be worth it.
Super-beefy control arms or magical flex joints are great, but if the vehicle bump steers, or handles funny because the roll center was only addressed at one end (if at all), or shears a mount...then I didn't get a well-engineered kit.
Having said that, aside from Poly, Currie makes a truly complete engineered kit as well...but involves some pretty heavy drilling and welding to complete. If you can do that stuff, or don't mind really ripping into the Jeep....that's a great contender too, and a bit less expensive than the Poly.