I have two older guns with the metal trigger guards and a newer SS/synthetic with a plastic trigger housing and they all seem to work just fine. My new Gun has an extraction problem and would not throw out the empty case. I bought a new extractor from Midway for about $10 and that solved the problem. I think the stronger spring was the real secret to fixing the problem.
I have read the metal triggers were not as precise and the people who assembled them had boxes of parts to try till they got it working correctly. The new plastic guards work without sorting through a selection of parts. Plus they are supposed to be more damage resistant.
Of my three the stainless is my favorite. I wish it would occur to ruger to make the buttplate removable so you could store survival supplies. I have been looking at the new take down model and think they missed a real chance for making a near perfect survival rifle.