THE LESS IS MORE !
Nowadays, many people just collecting VSTs like cars, books, music etc. In the past we had a few quality vst instruments/effects/sequencers and it was great (I know how paradoxically it sounds at first but belive me - it was great). Now there are thousands of them and many of you could quickly feel lost. Too many choices, definitely
So at first please take my advice into account and don't be plugins collector. Try to have minimal quantity of them. You will quickly realize how your composing / recording process improve and speed up. Get one drum plugin, one piano plugin, one guitar plugin, one or two synth plugins. Not dozens of them...
Now about orchestral plugins/libraries... EWQLSO, VSL, Cinesamples, Philharmonik, Garritan and many others... What you should buy? I always smile when someone say "(...) but I love to have many orchestral plugins/libs becasue I can layer them to get big sound". Sure, libraries are never perfect but if you buy one and master it, it will give you more than having arsenal of them. Remember - you are primary composer/musician, secondary computer/sound engineer and not inversely. Additionaly, even the best computer orchestra will sound poor in comparision with average recording of real orchestra, recorded in studio with Decca and spot mics.
The best libraries to me are those that cover all basic orchestral instruments/articulations with samples recorded dry (without reverb tail in samples) (like Garritan, VSL). You could easily tweak them and later put into any room with IR reverb like Altiverb.
In the past, I bought and used Garritan Personal Orchestra. Then I switched to VSL Orchestral Cube (GIGA edition which in the end I converted and programmend inside Kontakt sampler like old, good GPO). In 2007-2008 I also worked in the studio with EWQLSO Platinum. And you know what? If you buy/have Garritan or Miroslav or VSL or EWQL, you won't need to buy next orchestral product in lightyears from now
If something works for years, don't fix it. It's another very smart rule. Did Mozart complain about timbre and quality of an orchestra? Yes, he did. But... the emperor gave him one and he must lived with it
People are always very excited when new product / sample library appears on the music market. If someone would tell me that with Cinesamples or Albion or Symphobia etc. he (or she) could compose better sounding tracks than made with VSL / EWQL or even Garritan, Miroslav etc., I will just smile
Good lib + very good composer + great orchestration = ear's catching track.
The best, multi GB lib + bad composer + terrible orchestration = well... ear's cutting track.
So in the end, if you have a little in your pocket, buy Garritan Personal Orchestra or Miroslav Philharmonik, larn it, master and... live with this lib for a long time. Maybe one day in a future you could work with real orchestra and re-record your compositions? If you on the other side have money, buy one of big libraries like VSL or EWQLSO and I bet you won't ever be disappointed.
Last but not least...
It's subjective view but IMHO with Symphobia and Albion series we have turned into wrong way. It's cool to play and fun with them but from professional point of view these libs are just another toys in the synth's garden. They give good ensembles and just fresh timbres but never let compose classical music or compose in classical way, what is a big limitation. You won't have this limitation with products like VSL / EWQLSO / Garritan / Miroslav / Kirk Hunter libs...
Well, hope it helps, take care!

