And which ones do you use?

I guess the bench rest is where I always zero for training.

But when the hell are you ever going to shoot from a bench in the real world?  So if your checkweld is different on the bench, you may not get a perfect zero.

I shoot NRA Highpower and regularly shoot load development and accuracy checks.  I can shoot a 20-shot string or two from prone, but it's much less tiring using a benchrest and scope.  I may shoot over 100 rounds when I'm doing full-blown load development.  I use a Midway rest, which has fewer features and is lighter than would be used in benchrest competion, with a bunny-ear rear bag.  Since benchresast isn't where I compete, a full-blown (expensive!!) setup is of no use to me.  I need to know whether my rifle is shooting ~1/2 MOA at 300+ yards - I never try to get smaller than that.  However, John Feamster was able to shoot an "official screamer" in bechrest competition - ~1/4" at 200 yards IIRC.

I use my Harris bipod to zero in.  I call it "real world" zeroing.  :)   I figure that is how I am going to use it anyways, so I might as well get my zero down accordingly.

Wes

i use a sinclair bench rest.  the best out there IMO
Remman

I clicked without an option. None . If we are talking AR's here, I prefer to sight in with my elbos on a bench, rifle in my hands.
Bolt gun, My rimfires I enjoy shooting from a rest front, and body support rear. My varmint guns shot from a 9-13" Harris swivel collapsed to 9" and if using the bipod from the bench, I put a towel under the bipod and suck up the height.  

Loop sling

Harris bi pod.