panzer campaigns - bunkers

[CheerfullyInsane]

Depends on a lot of things.

First, do you actually need to take the hex? If not, bypassing it is usually the way to go.
E.g. the defensive lines in Kursk have bunkers flanked by trenches, so you're far better off attacking the trenches instead.

If you have to take the hex, surround and isolate first. That drop in morale is kinda important.
Only exception is if you're fighting Japanese. Fanatical units won't surrender when Isolated, so it's better to push them out of the bunker first, and kill them in open terrain.

Next, you'll need to Disrupt the defenders, which means heavy artillery if you have it. Hard targets hit by artillery has double the chance of Disrupting units, but since Disruptions are dependent on causing casualties in the first place, you need some big tubes.
Alternatively, anything with good Hard Attack values. Tanks, AT-guns, heavy AA.
Air attacks with good Hard Attack is another option, but they're fairly rare.

Once Disrupted, you can consider the assault.
Always use units with the highest morale you can find.
The rest really depends on whether you have the Alternative Assault optional rule turned on or not.

Without it, look for units with high Assault values. Engineers, flame-tanks etc.

If Alt. Assault is on, you have to use tanks to assault. Only bring enough infantry to avoid Combined Arms penalties.
Since the infantry won't have any effect on the assault itself (since they usually have very low Hard Attack), it makes no sense to bring high-value infantry to the party.
Just note that the morale of the assault-resolution is based on the LOWEST value in the assault, so don't bring infantry with lower morale than the main armored units.

All in all, bunkers are a b*tch to deal with. With Alt. Assault on, they become even harder.
And digging high-morale units out of them is an exercise in futility.
So bypass them if at all possible.
If that isn't feasible, be prepared to spend a lot of assets and time on them.