Lionel Lizardbane:
I'd personally go with levitate. Stinking cloud is great, but depending on your DM you might just have monsters run through it whilst holding their breath or something else that they metagame to reduce its effectiveness.
Yeah I don't think that would wash when the spell says creatures caught within the spell area MUST save versus poison and the spell effects visual and olfactory organs as well. In reality (IMO) Stinking Cloud is far too powerful to be level 2.
I'd always go with Stinking Cloud because I like spells that can't be saved against. Levitate is neutralised with a successful saving throw, Stinking Cloud is still effective even if saved against.
Creatures that emerge that make their saving throws are still helpless for 1 complete round. That's helpless. As the DMG says pg 167
DMG:
"In totally immobilised and power-less situations, the opponent can be fully trussed, slain, or whatever in 1 round."
Stinking cloud can be a kill spell even to creatures far more powerful than you and when a mage of mine has one he usually always carries it in reserve for emergencies. Get yourself a Necklace of Adaptation and you become a killing machine since you can dump the spell upon yourself and remain unharmed whilst everyone around you is spluttering and choking.
Levitate might seem useful but it is seldom used.