I use both, depends on the season and where I'm going.
I like a poncho in the summer. Raingear down South carrying a pack while hiking? Well, choose you poison, you will either get soaked from your own sweat in the jacket/pant combo, or get a little wet from the rain with the poncho. I'll pick the rain over my own sweat anyday in the summer.
In the winter, different story. I like to stay really dry when it is cold, so I'll go with a jacket/pant combo. I'll wear this when it is cold enough to not soak from the inside-out during moderate activity. Sometimes I'll do the poncho/rain pants combo.
Edited to add - Sometimes in the summer, it is so stinkin' hot here, I just plain don't worry about raingear. I look forward to the cooling effect of a light rain. All situational, of course. I realize you can go hypothermic even in the summer from a good soaking, I'll only do this if I've got dry clothes and shelter as a backup.