spellbreaker
shield of solitude
or shield of Ysgramor

I dont think dragons can equip shields.

Regardless of what ppl say about destruction, I found out that using dual cast perk to stun the opponent with destruction is the best way to take down dragons because you prevent them from shouting. Also after shocking them a few times they take off and by the time it lands again you got full magica. Rinse and repeat. I got out of most dragon encounters without a scratch. Now I'm dual casting expert lightning bolts 2x75 damage without breaking a sweat. I doubt bows would be that effective and you will run out of arrows eventually.

Doesn't really matter, if you are using a shield against dragons it serves two purposes. First enable the use of the perk to reduce elemental damage by 50%, the second is to shield bash the dragon so it can't do [censored] while you kick it's ass the type of shield doesn't really matter for either of these. The choice of shield pretty much entirely personal preference.

Edit: Also your stats get high enough end game that choice of equipment is more about what you think looks good than any real statistical advantage.

Use the spell breaker. its ward effect will prevent all damage from a dragons breath attack as long as you get it up in time. Not even elder dragons can break the ward.

Spellbreaker isn't powerful as some ward spells but at least it doesn't drain magicka really quickly.