I have my music somewhere here? I usually try and avoid that
I love them both. I love Alex and I love the guys at Spitfire.
My personal take. I don't own any CSS. I wish I did. For some reason though the section size of the strings and the smaller brass room just haven't quite hit the mark. The timber of the strings isn't really for me but I will at some point get the brass and woodwinds though. I judge this just from the demos not from user experience. But, many, many people I respect love CSS so you can't discount it. I'm weird. I don't hear music right. I certainly don't hear what others hear. I've learned to live with my shortcomings and play to my strengths which lead me to BBCSO.
I bought BBCSO core just to try it out. I love it and as soon as finances allow I will probably upgrade to pro. I grew up listening to concert orchestras rather than 80's and 90's film scores and BBCSO has that definitive concert hall classical sound. Some people think that it lacks loudness. Nah, if anything it lacks softness imo. But, if you grew up listening to 90's Media Venture scores then it won't be loud enough for you if that's the sound you're after.
That being said, BBCSO isn't for everybody. You really do need to know a bit about orchestration to get good results. I think CSS is a bit more forgiving in that regard.
Truth be told if you're starting out I wouldn't just bank it all on just one library. Each library has its strengths and weaknesses. If you could swing it, I'd give BBCSO core+ at least CSStrings and CSB. That would be a killer combo. Then when money permits get BBCSO Pro and the rest of CSS.
Be warned though BBCSO is a very wet library so you'll need a good reverb to match your CSS libraries to it.