I think the best way to word Sul Drinker would be:

When ~ enters the battlefield, sacrifice a creature. When you do choose one ó
  • For each +1/+1 counter on that creature, gain 3 life
  • For each -1/-1 counter on that creature, put a -1/-1 counter on target creature


The modal part means you donít need a target if you sacrificed a creature with +1 counters, and the reflexive trigger means you donít need to make that choice until youíve actually sacrificed the creature.