EXS 24 Logic Sampler Users Group

I'm interested in purchasing some more sampled instruments for the 
EXS24. 

With only a single SampleCell CD, I have no experience with the 
alternatives.  I like the fact that the SampleCell CD has multiple 
velocity ranges for the keys. 

1. My interest is in acoustic instruments.  Of the sample formats 
available for importing, which is best for providing realism?

2. Are there some preferred vendors which provide top quality samples 
(well, maybe not top quality, I'm only an amatuer - possibly my 
criteria should be 'best bang for the buck').

Thanks, Les Caudle