Each developer has a slightly different sound to their library. I often combine EW with VSL and most of the time it works very well. The legato instruments of VSL compliment the excellent percussion and brass from EW.
Project SAM was one of the earliest libs I bought and I often combined them with EW Silver, Prime Sounds Session Strings, and HALion String Edition 1. Their brass also sounded excellent. Because they record them with different mic positions you have make sure you choose the right one.
Symphobia is quite the talk of the town these days, especially when you can go to TrySound.com and play around with the sounds. I wasn't convinced until I went to that site, loaded some brass and string ensembles and was blown away. I actually recorded a short demo that can be found in the listener area of this forum.