I love Justified. It's my favorite TV show without question, even against all the other great ones like Breaking Bad.
My favorite part of Justified is not the particular mechanics of any gun or how it is handled (even though they're generally, as mentioned, pretty darn good about it), but about how the gun does not make the person like it does in every other TV show. The show properly displays the ubiquity of guns that is true where I live in rural WY and I know is true in most of the South. The bad guys aren't always afraid of them, the good guys can't always use them, and their presence in a scene is usually an accessory, not the focus.
In other words, despite the heavy presence of gunplay, I think it's one of the best shows on TV for the axiom "guns don't kill people, people kill people".
It doesn't hurt that Olyphant is a skilled and likable lead or that the plots and dialogue are very well-written.
If I had to pick an eye-roller moment from the show, it'd be from Season 3 where Robert Quarles is talking about how deadly his .32 ACP hollowpoints are.
Probably the worst show I've seen in terms of heavy-handed political talk about guns is Law & Order SVU and the other Law & Order knock-offs.
For lighter comedy TV shows, even though they acted like it was fringe and weird a few times, I enjoyed on How I Met Your Mother that Robin's gun hobby was mostly portrayed as a healthy stress outlet and way for her to not have to be afraid in the world.