What weapon do you use when your character is at a high level?

Daedric Bow.

My last character ended her career with the Bloodskal Blade.

It's normally a Dragonbone Sword with a Paralyze enchantment.

My forsworn character Valeria uses Dragonbone mace combined with a shield. Her bow is a Dragonbone bow with steel arrows.

My vampire thief character uses illusion and a skyforge steel dagger.

For my good play through , I use a Blades sword called Blades Divinity with a powerful shock and paralyze enchantment.

For my more evil play through. I use a deadric sword called Inferno with a powerful fire and drain health health enchantment.

Stalrhim Claymore/Battleaxe Enchanted with Chaos and Frost Damage. I always call the Weapon "Wrath of Nomeg Gwai".

Where do you pick up a Daedric bow?

craft one with the smithing perk daedric armor/weapons or loot them from high lv draugr. I've managed to find daedric and ebony items on draugr once I was above lv 40.

I always make it through Smithing. Like Resident_Within said, sometimes you can loot them from high-level Draugr. I got it off Dragons too.

Depends on the character. My latest character, a Nord with a playstyle not too different from that implied of my current profile picture, ended up using the same steel warhammer he forged when in Riverwood after having escaped The Weekend. Not enchanted, merely tempered. Ended up at Flawless or Exquisite. Didn't invest all that heavily in smithing on that character, only to the point where I could get Steel Plate armor. I did enhance my damage a little though, by enchanting a +13% two-handed damage ring for myself. Only enchanted piece of gear a had, except the Charmed Necklace I got as a gift from some friendly travelers I met on the road.

Worked well enough on expert difficulty.

Daedric bow and axe.