Paracord
Better strength*/diameter ratio. 550lb paracord is 5/32" (4mm) in diameter generally. Twisted poly of a comparable strength is around 3/16" (4.75mm). So the paracord will pack smaller.
More versatile. You can easily divide it into multiple ropes. Its form also makes it much easier to braid than twisted poly if you need to make a stronger rope.
Easier on your hands -- If you've ever tried to hoist a heavy pack with twisted poly you know that stuff eats skin. The smoother paracord is less hand-shredding.
Twisted Poly
- Cheap-er (about half the cost) - Paracord 1000ft/$50 (0.05/ft), Twisted poly 1200ft/$32 (0.026/ft). I say cheap-er, because paracord isn't exactly what I would call expensive.
*Strength = maximum load strength.