Lightning I too liked doing LDoN's with my 67 Dark Elf Necromancer Seuin Deathweave. I had a Cleric friend who helped me get some nice items for my necromancer. My favorite tank was the ShadowKnight because they could take agro and keep it forever. With a ShadowKnight tanking I could stack 5 of my biggest dots and spam my biggest life tap and never get agro even with a mage buffed spectre
We got to the point where the cleric buffed and did melee most of the time, hell our clerics often times dusted off their Direct Damage spells *grin* I could even life bond the SK and give him/her 500hp a tic for 10 mana a cast.
I would chose a longsword for my Dread Knight because I like the balance of speed and moderate damage.