I personally have never used Spitfire Audio’s stuff, but I hear it’s very very good.
Native Instruments have been a god send for me, especially their Sunburst Electric and Acoustic Guitar virtual instruments. If like me you aren’t a competent guitarist these are really invaluable. They’re super easy to use and they won’t breaks the bank.
If you are looking for orchestral stuff, a tip: I have Kontakt with a free version a free trial package of loads of sounds. There’s no limit on the trial datewise, but you can only use it for a small period of time (10mins or something). It takes a bit of planning, but what I do is arrange everything, record it in, then bounce it down as .wav so I can keep it forever in the track. Free Kontact Orchestra!