VSync - On or Off?

off always

Ummmmm, depends on the game.

60hz screen - on

100hz - off

Usually ON to prevent tearing and overheating due to a runaway framerate, except in one or two games that drop below 60fps (Far Cry 3 on Ultra settings comes to mind.) Lately though I've been using neither on nor off, and instead dabbling with Dynamic Framerate and Dynamic V-Sync.

On, caps my games at 60fps and puts my rig under less stress

on.

I have it on because I have tearing in pretty much every game without it.

Always off, In some AAA-titels i get screen tearing and then i turn it on.

It doesn't seem to do anything except cause lag, so i turn it off.

Always off apart from old games.
For example removing it for Thieves : Deadly Shadows will bring a lot of collision trouble when climbing walls and opening chests when off.

On, if i have it Off my fps climb too much and my card does a weird high pitch noise

I'm not sure what it does exactly but I always turn it off because my GPU is crap.

I turn it off. With some games you get a bit of lag (like CSGO) which can make the game almost unplayable

Both
It depends on the game.

i dont have those problems simply becouse i have a shitty pc and i get most 30fps in games. hell even left 4 dead 2 on low with 640x480 is lagging :D

In games like RAGE, it's pretty much necessary cause of the massive amount of tearing.

Always off,tbh, I do not mind tearing

I have it on all the time as long as it doesn't make the framerate drop too much of course.

I always turn it on, and if the game doesn't have v-sync, I turn it on in the nvidia control panel, I just can't play a game if it has screen tearing.

Off.

I keep it off unless screen tearing is pretty distracting. My PC is pretty dated so I need every extra frame. But lately I've been very sensitive to screen tearing, so I usually turn on Vsync in Radeon PRO + Triple buffering to reduce any framerate drops, and it's usually better than in-game Vsync.

However if I'd have to choose between screen tearing or lower fps/jerky mouse movement, I'd go with screen tearing.

off = fast

if your pc can handle vsync then it helps to eliminate screen tearing (horizontal lines that appear and disapear quick)
untill i built my last pc i could never turn vsync on as it would cause my fps to drop so much it was unplayable, that was cause my video card wasnt able to keep up and supply a constant framerate so it was a bad thing to use vsync.

with a good enough card it can be a good thing. even then tho i usually only use it in single player games where i see screen tearing, i try not to use it in multiplayer games especially shooters cause of input lag it can cause.

on

In some games, I turn it on (Borderlands 1 for example).