The Fledermaus III and the Ludwig cost roughly the same points (43 vs 40) and are both capable of taking out enemy armored units.

The Ludwig has unlimited range on its main gun and rolls more dice against Amor level 5, 6, & 7 units. It can also take advantage of cover on the battlefield to prevent itself from being targetted.

The Fledermaus only has range 4 on its weapons (but it can't be attacked outside of range 6). It also can't perform sustained attacks. Nor can it hide behind cover. However, it has move 3, can deploy almost anywhere on the battlefield, can move over any type of terrain, rolls a few more dice against Armor level 1-4 units, and rolls significantly more dice against infantry and aircraft. Oh, and it has two more health as well.

If you could only have one in your Axis army, which would it be and why?

The Fieldmaus wins hands down for me as nothing is safe from it and apart from dedicated AA units, is almost invulnerable so doesn't need to hide. I would pair it up with the MkIV though to take on the heavier tanks.

Agreed, F,edermaus is my pick also.

Ludwig can be targeted by more uni than a Jet which can only be targeted by anti-air units. Machine usually will not be able to take it out unless its only at 1 or 2 health.

Hopefully Fledermaus won't be the only unit in your armor that is anti-armor and I think you will be fine as I think Fledermaus can do way more damage to infantry unit. Which is probably the most numerous unit on board most of the time.

Ludwig can be targeted by more uni than a Jet which can only be targeted by anti-air units. Machine usually will not be able to take it out unless its only at 1 or 2 health.

Hopefully Fledermaus won't be the only unit in your armor that is anti-armor and I think you will be fine as I think Fledermaus can do way more damage to infantry unit. Which is probably the most numerous unit on board most of the time.