2 bulbs 100W each, both driven normaly, one is 12V, other is 120v.
wich one will be brighter, or does it matter at all?
Depends on bulb life and bulb type (Halogen, Argon and...).
If bulb life, bulb type are same and both driven correctly, total output will be pretty much same.
Size and shape of fillament will effect on beam shape.
It is obvious that size and shape of two above bulbs will be totally different.