VSamp is cute and lean and works well. to create programs, use the standalone.
but mind the formats it reads and and that you can not really import bought libraries in regular formats.
with giga import and the drag options, keyzon editing and stuff, halion has a point. but if i would use samplers i would hate halion for having the filter and envelopes not nulled in def patches.
CPU friendly and easy to use synthesizer are PPG - and FM-7, if you know a bit how to operate FM.
best sounding synths are probably oddity and imposcar. the latter is not 100% stable in OS9.
best sample instruments are IMHO plugsound, presonus orchestral, the roland GM modules, kontakt 2 factory content and kontakt piano.
worst are the grand, USM, VGEE and everything sampletank.
best freeware plugins are mda piano, linseners free alpha and ferarris FM heaven.
others i like are synapse scorpion, TC mercury, LM-4 mkII, Dacota, Slayer, Albino.
as for samplers, you should see if you like the emagic.