After making a Summoner roughly 5 times, I preferred Life Tap because my minions almost never died. (some would die on occasion with those Lightning enchanted monsters)
Amplify Damage = Big radius. Benefits your Skeletons and Revives.
Life Tap = My minions rarely died, but slower kill rate. Better safe than sorry in my opinion.
Decrepify = Radius is too small and mana cost is a bit higher, though I may try it this time around.
Lower Resist = The only curse that is good for PvP. Cast Lower Resist and revive a bunch of Lost Souls. (those lightning ghosts)
Any other curse sounds useless. ;)
I do see some Summoners use Corpse Explosion, though it's not my style.