either, depending on the situation. A good prone position off the bipod with a rear bag is preferred, but often not possible. Lately, I've been practicing and trying to become proficient from seated and kneeling positions with a short Pig tripod and saddle, with a large lightweight Traust positional bag to fill in the void under my strong side elbow.
I've found that the shorter Pig tripod for kneeling/sitting shots is realistic. However, you need to spend a whole lot more money on a way better tripod if you want to hit anything from a standing position at longer distances (400+ yards)
Only you can determine that, based on how and where you hunt long range. Type of terrain, coupled with the conditions can be a game changer.
If you hunt from stationary positions, especially the same ones year after year, you can usually adapt the locations to suit your preferred method at least to a point.
The vast majority of all PA long range hunting/shooting is from some type of bench. Be it piled up rocks, a board nailed on a stump, or a small portable one carried to the location.
It would be rare to hear about someone preferring prone/bipod there primarily due to terrain and other restraints. So to sum it all up, conditions will decide that for you to a large degree.
Where I hunt, with the terrain and vegetation I can't count on being able to set up prone. Hammering off a bench or bipod is lots of fun, but if I'm training to be able to make the shot on game I'm working on stable seated position with tripod/saddle, pack tucked under right armpit, and eating humble pie after thinking I was hot stuff off the bench.