the highest physical damage weapon is the 2 handed blade of umaril: x000f35. add 2 of these items via console; the game will strip 1 and leave you with a 100+ damage weapon. using a 2 handed weapon with a shield is possible, however, blocking will not reduce the damage that having a 1 handed weapon will.

the highest physical damage of a 1 handed weapon is umbra. umbra's quest item can be kept, however, disallows a 100% completion.

physical damage at level 30+ and on hardest difficulty simply won't be enough. your weapon will break long before a mudcrab dies (practically).

a custom enchanted deadric long sword can effectively simulate magic stacking - creating the largest damage by far. magic stacking without the sword is better since it doesn't require recharge management or armorer.

at levels where being staggered or knocked down become commonplace, magic stacking becomes unreliable.

many enemies either have reflect magic (making the stacking dangerous) or have enough resistances that it's simpler/faster to use poison. poisons make all weapons exactly the same - no weapon will kill any faster than any other weapon. as such, the most desirable weapons are weapons the enemy can't take.

weapons that can't be disarmed are quest and bound items. bound items can disappear at inopportune times and quest items tend to become non-quest items once the quest is finished. there's only 1 quest item that maintains its quest item flag after the quest and incidentally is a dagger - allowing the fastest recovery and poison application time to multiple targets: the fork of horripilation. the fork has the unfortunate side effect of shutting off magic regeneration when you equip it. if you unequip and re-equip it, your magicka will regenerate as normal. anyone know of other permanent undroppable items that don't alter quest completion?

I am at level 46.
UMBRA makes 33 damage only (having soul trap enchantment) with use 2500

GOLDBRAND makes 30 damage + 22 pts of fire damage!!! Use 3000.

So, for me. the best is Goldbrand... Both Umbra and Goldbrand may also be found in Morrowind.

Frankly, it depends on the character, not the weapon.

Also, I would not say that "many enemies" have reflect magic. Some do... but not very many. I play pure mages with no problem at all, really, even at higher levels facing Xivilai, Golden Saints, etc with reflect. You just have to be properly prepared, magically, just as you do at lower levels with enemies such as Will-'o'-the-Wisps.