CCL: insightII/discover vs CHARMM



Hi,
 Can someone tell me the pro's and con's of insightII/discover vs CHARMM?
 I have used insightII/discover, but most people here seem to use CHARMM. Wonder
 if you guys can explain for me the difference, in terms of the pro's and con's?
 And if any reasons I should switch to CHARMM?
 URL's discussing these are appreciated too.
 Thanks,
 Yao