Strong preference for jacket and pants. I tried a poncho for a while after seeing them in widespread use in Vietnam, but I think it is far inferior in general.

Poncho pros:
- Quick to get on and off
- Cooler

Poncho cons:
- Dosen't keep legs dry
- Still get wet from road spray (even with good mudguards) at anything over 15km/h or so
- Flaps around in the wind
- Loose ends can get caught on seat if elasticated, or can fall away towards wheel (never got it caught in the wheel)

Fine for short tropical downpours when cycling at walking speeds amongst many other cyclists. No good at all for commuting at speed in city traffic.