Be aware that this list may contain mad ****SPOILERS****
My first top ten list is going to be a short list of the weapons that I still think of to this day. Basically, means of killing enemies that have made an impact on me, causing me to reflect and think "Okay, yeah, that was awesome." Sure, there are a ton of these lists floating around, and I'm sure that you're likely able to predict a few of them right off the bat...but I'm hoping there'll be a few surprises in here. Just bear in mind that this is my personal opinion, of course, and the selections I choose may not be as obvious as one might think.
The biggest problem is figuring out what order to put the damn things in, as a number one weapon of all time is extremely hard for a gamer who started back in the 80s to decide upon. A game with weapons is, in my opinion, defined by that weapon set, since they're clearly the tools that you're going to be using the most to get out of sticky situations. The right tool needs to be chosen properly...but then at the same time, maybe a game player establishes a soft spot for a weapon that's not entirely convenient but tries to make the best use of it. This is one of the tough parts of weapon selection...finding that balance between what's useful, and what you just plain enjoy using. For example, I don't want to go through a modern shooter using 76 different kinds of machine gun with different fire rates and recoil...that just becomes boring for me, but I know that certain gamers prefer to pick the most efficient weapons. Personally though, I tend to use the oddball ones just because they're fun...even though I might send myself to the grave with them more often than I likely should.
Anyway, on to the list.