Which strategy is the most efficient for Clickers?

I try to avoid them at all cost. Just sneaking by them and kill as little as you can, if possible. That's what I've been doing and it's been effective, though maybe not as fun, but it gets the mission done. This way, you save on supplies. If I HAD to kill and fend them off, I usually use a shotgun or a handgun since I like those the best.

While Rob Avery's suggestion of avoidance is a valid one, I usually took it as a challenge to kill all of the enemies in an area before moving on, so I needed different tactics. I was also stingy with my shivs so barely ever used them other than as a rarely used emergency escape from clickers (with the skill) or to open doors that required shivs, so stabbing them all in the neck was out for me.

I found arrows to be really effective instead, at least on the unaware clickers. Most of the clickers you face throughout the game are easy to get close to without raising an alert, and it's usually trivial to get close enough to plop an arrow into their face, which is a nice, silent instant-kill. Just save your arrows for this purpose... they're overkill for humans, which you can just strangle, or runners, which are usually easy to melee unless they swarm you (at which point, you aren't going to want to use a bow and arrow anyway). As a bonus, you'll sometimes be able to recover the arrow after the kill.

During those occasional times when the clickers are aware of you and charging endlessly, the shotgun (if you wait until they get very close) or the rifle worked best. On hard, the rifle was often a one-shot kill even if you don't hit the head, and upgrading its ammo capacity was a big help if you needed to take out 2 or 3 in a row.

Lastly, while it costs 75 drugs (or whatever it is you buy skills with), the skill that lets you get a clicker off of you with a shiv can be a really big help. I recommend that if you plan to get it you get it as soon as possible in the game though, because it seemed to me that close-quarters fighting with clickers was a lot more common in the early and mid game than the end game. Given that without the skill a clicker's touch usually means death, it's nice to have on some of the tougher fights, particularly if you're playing on a harder difficulty where ammo is scarce.

Though you have to get close, I like to use a brick as a melee weapon. Using a shiv, pistol/long gun, pipe/plank etc. works, but at the cost of precious supplies. Since bricks are so ubiquitous in the game, it is an option to dispatch the Clickers and preserve those supplies for something else.