I'm growing more fond of the "bull bag" when sighting in and checking for accuracy.
(The item I actually use is:
Caldwell TackDriver Shooting Rest Bag; $33 'filled' from MidwayUSA)
The rifle and bag 'become one' and when lined up, it is easier for me to adjust the elevation without disturbing the gun itself. Also, the gun recoils in a straight line without coming off/out of the bag. It is 'repeatable' to use. It is steady. It allows the gun to recoil in a more 'natural' way (vs. a bipod which has no 'give' in the downward direction.)
I'd shoot off a bipod if I was going to use it in the field hunting though. Best to sight in and shoot the way you will when hunting. Once I'm sighted in using the "bull bag" I then fire a group with my hand under the forend (between rifle and bag) so I'M THE ONLY CONTACT on the rifle as that will be how I shoot it when hunting. I want to make sure the gun shoots to the same spot it shot from the bag itself. It almost always does. Almost. Every now and again, I need to make a small sight adjustment for a very light gun which 'behaves' a bit different in my hands vs. in the bull bag.
I've done front rest (sandbag "V" or "U" rest) and rear (sand)bag setup. It works fine. The reason I'm not using this setup as often now is the two bags (front/rear) are not connected and a hard-kicking rifle throws the whole setup off with each shot requiring too much fiddling around to get things lined up again for the next explosive event. Minor thing, but the "bull-type" bag just seems easier/faster and less 'fiddly' to me these days.
When at a range that allows it, I love to finish my shooting with some off-hand shots using the sling to see how far I can keep things inside a paper plate. Many times when hunting, the animal is suddenly there, has spotted you, and the shot needs to happen NOW. I like to KNOW I can make that shot when needed. Benches are great for sighting in and showing off small groups to your friends, but it's the off-hand shooting that really pays off once the sighting in is done.