The first is the best. Having recently watched (at least the opening part), it's amazing how much subtlety is in the 'intro' dialogue, makes the characters seem natural. Also, of the four movies, possibly the least preposterous, and certainly the least 'over the top.'
2 is over the top in the set up. Ceramic glocks, ATC/ATM, and a whole host of other things are given 'artistic liberty' in order to make it work. Yes, it hurts my head to think about the errors/"liberties taken", but it's easy to maintain 'suspension of disbelief', and I would argue that 2 is easier to watch (for me) than With a Vengence.
With a Vengence is, of course, still fun, and I'm not going to refuse watching that movie. There is still quite a bit of 'glossing over'/'creative liberty' of things, like in Die Hard 2, but it gets a pass because again, it's easy to maintain 'suspension of disbelief'.
The first three movies were fun, had tension and drama where it needed to be, but stayed toungue-in-cheek with the dialogue and witticsms.
4.0/Live Free or Die Hard seemed a bit pretentious, like it wanted to be gritty/dark in a series that's generally been fun. And it seemed like the script writers didn't understand the character of John McClane. I felt it lacked the fun, witty banter, and replaced the classic "Oh SHI-" moments with stupidly over the top stunts and explosions. In the first three, McClane seemed more like an average Joe in an extraordinary situation. And every stunt had a real sense of danger, that if it didn't go right, our hero would be quite dead; and further more, these stunts were not something our hero did as his day to day routine. 4.0 seemed to lack that sense of danger, even in the overly rediculous stunts (like the Semi-truck vs. JSF fight). It seemed less "what would someone like our hero do in this situation" and more "wouldn't it be AWESOME and EXTREME to fight a JET PLANE with - get this - a SEMI TRUCK!! Oh, but we'll make the rest of the movie gritty and emo, because obviously everyone who were huge fans of 1,2, and 3 fit into that demographic and aren't old enough to remember Moonlighting or Hudson Hawk."