Depends hugely on what type of character i'm playing with. To be honest i leave them alone these days unless i'm wanting the experience boost.
A very low level high elf with ice spike can destroy a giant quickly using their greater power as long as said giant doesnt have mammoths or other giant friends with it.
I've only killed one giant; I normally leave them alone. But on this occassion, a dragon upset a giant, and he came too close to me (I guess he was chasing the dragon). I tried to stay away from him, but alas, when the dragon died, the giant came after me. I ran (playing a c. 28th lv. character, on master, with dead = dead). He persued me all the way to Whiterun - I thought he would give up the pursuit, but he didn't. The lousy city guards ran - so I was forced to take him out, by myself, with my bow. I had to fire once or twice, sheath my bow, run, fire again, and repeat, until he was dead. It took dozens of arrows, plus several stamina potions/food.
Sneak attacks with a bow and a nice rocky perch to slow him down.
But I rarely kill giants anymore. I stopped taking jobs for one of the Jarls when I realized that he probably wanted me to kill every giant in his territory. It seemed kinda short-sighted if they ever take offense.
Ice spike is my friend. :)
Start at a decent distance away, obliterate their stamina and as they casually walk up to me keep on with the spikes. Reposition as needed. SPIKES AWAY!
Killed a giant at something stupid like level 3 with this... took a while true. But I did it.
Flastie has been taught well (or is a Quebecer like me!).
Having tried various poutines from various reknowned places in Quebec, it is with pride that I tell people that the best poutine in the known universe is made in my hometown of Longueuil Quebec at "Alfa Hot-Dogs", on the corner of Chemin Chambly and Beaubien!
In fact I think I'll go have one over the weekend