Music Composers Unite!
Some (most) would say Vienna for a complete package.
I would say LASS2.5 (for strings) together with Berlin Woodwinds and Brass. Timpanis and cymbals from someplace else.
It depends what kind of sound you want. For a more classical sound VSL (best one if you want many articulations), LASS, Berlin Woodwinds are all very good (and can also be used for a more cinematic sound). They are quite dry, which allow you to shape their sound how you want. But I think that the current top "wet" (recorded in a big hall) sample library developer is Spitfire. EastWest's Hollywood Strings is also an awesome library, but you will need a VERY powerful computer and a big SSD to run the samples.
I can only speak for myself...Normaly I shy away from entertaining "the best"syndrone, but ............
I use Berlin Woodwinds, Cinematic Strings,CineBrass Pro, and an old VSL pkg (Opus) for percussion and various misc.
Thanks to Per_Erik, Bernard and Vincent so far! I'd agree with Vienna... but way out of my league (though I did get to conduct a Vienna orchestra recently and that was a real blast!). Has anyone tried Komplete?
Other suggestions welcome.
I use Cinesamples Drums of War for ethnic percussion. The majority of my music is electronic-infused, so I'm not as concerned with getting the typical "classical" sound. The native samples that come with Kontakt are quite good, and very easy to edit to get the sound you want. The full Kontakt VST also comes with an ethnic library, orchestral, band sounds, organs, etc. too much to name. My main synth is also Omnisphere, which besides its electronic elements has great string sounds!