I'm generally going to say muck. I don't typically show my cards, but I'm never going to show a bluff. If, and when, I do show, the reasoning is twofold.
First off, some players become hyper defensive and will re-raise you all-in if they think you are just trying to steal their blinds. I myself am sometimes suspicious of late position raises. In a situation like this, where I may have raised with something like A-10 off, but am not willing to risk the majority of my stack with it, I might fold it and show it to remind the players at the table that they need to respect my raises because I'm not raising light.
Some of you might wonder why not just muck and move on. This brings us to the second reason for showing. Actually the two work in conjunction. Going back to the example above, A-10 offsuit may notbe worth calling an all in for the majority of my stack to me. But to other's A-10 would be a snap call. When they see they see me lay it down, it gives them the mistaken impression that I will lay anything down if they move all-in on me, which isn't the case. But having my opponents have this impression of me tends to come in handy later when I want to lay traps with monster hands.