as tyree and josh noted, there is a lot of misinformation out there, coupled with the fact that there is not much CURRENT science being carried out on these corals, with the exception of J. Reimer's work in Japan
from my experience:
Palys
-wider diametre oral disc
-muted colours - earth tones, greens,
-more readily accepting of meaty fare such a mysis and cyclopeeze
-incorporate sand particles into the coenenchyme
-very hardy
Zoas
-smaller diameter oral disc
-high degree of variance in colours and patterns....very colourful specimens hail from places such as Solomon Islands, Fiji
-they exhibit a feeding response when given foods such as mysis and cyclops, however it is unknown whether zoas actually take the food in....it's believed zoanthids are primarily phototrophic
-very hardy, but to a lesser degree than palythoa
Zach