These Kirk Hunter Virtuoso Ensembles are my new favourite >
https://www.kirkhunterstudios.com/products/virtuoso-ensemble/ They are also on 70% off sale until tomorrow ($89 instead of $299) and take up less than 3Gb of disk space.
I have been using Miroslav Philharmonic CE (
http://www.ikmultimedia.com/products/philharmonik2ce/ ) and EastWest Hollywood Orchestra Silver (
http://www.soundsonline.com/hollywood-orchestra ) before this, both of which I like but Miroslav is easier to work with for a quick ensemble part IMHO. These are the entry level products which still sound good enough to my ears as I am not using them to make a living.
You can spend more (lots more in some cases) to get better quality e.g. Gold/Diamond versions of EastWest products and full Miroslav but the entry levels might suit and also check the disk space required by the pro level libraries.
Others can probably advise on the more Pro level libraries.