Totally dependent upon the type of training is in line for that day. For my unknown distance long range shooting, we use a 20"x20" steel gong. Our current range allows us to engage it anywhere from about 400 meters to 800 meters.
For zero and known distance shooting, I tend to use orange dots from 1 - 3" on cardboard. For known distance out to 1000 I use the 1000 meter competition targets.
I do have various other targets also, some of faces showing brain stem, others that may just be dots or squares. Of course, for a change of pace, we like to bring out ballons to move in the wind, or eggs, etc. Some of my favorite (but don't get to do very often) is to tie up flash bangs at 500 meters. Yep, they actually go off when hit... its great fun.