What I've found in VSL is that there are many variations of mild vibrato and intense vibrato to use. There is an espressivo vibrato ff to contrast with the pp mild vibrato.
Though I must caution you, that in this first edition, though the samples are incredibly beautiful, they are actually not as detailed as Garritan. Though VSL is in the pro edtion going to remedy that with more samples.
But I would add that I love Garritan's light attacks - the spiccato and sautille, including up and down bow variations, that I don't see in Vienna yet - though I am certain they are going to do many more samples and include those.
I hasten to add that the dynamic variation of Vienna is immensely superior to Garritan. I was extremely disturbed by the coldness that the pianissimo strings of Garritan in all the instruments have and the lack of "dry expressiveness" (that's the only term I can think of). Vienna truly captures these, while Garritan doesn't even come close to a genuine pp.