Most of my German hunting friends use a 308 or 30-06 as their primary boar gun as easy to shoot. They might reach for their 9.3 if very large boar are expected.
A good tough bullet and a rifle that handles and points like a shotgun, that fits well and shoots where you look is far more important than calibre. Some like red dot sights. I prefer a 1-4x20 scope.
In Germany the min legal is 6.5mm cal and 2,000 joules of energy at 100m.
In terms of action type, bolt action is most used along with straight pulls. Both can be reloaded fast, but realistically you have one shot, so make it count. Most of us cannot reload fast enough to get a second accurate shot at a group of piggies run through the woods. If you want an immediate second shot then its a double rifle that is needed.