1. By and large Studio is to be preferred over Live.
2. There are many orchestral recordings in 60s that are great. This was a time of great optimism in Europe and it comes out in the playing. This typically means that you have to go for LP.
3. The popular orchestras and popular conductors are generally safe bets. The trick is the smaller labels / artists. A striking example is Sibelius Violin Concerto performed by Dylana Jenson with Ormandy conducting the Philadelphia Orchestra. (LP version only, I'm afraid). Another is the Punkt Label that put out Haydn Symphonies. Just too many to mention.
4. Hi-Rez (not more that 96Khz) is often good.
5. Be aware of reissues. For example the Sibelius mentioned is disappointing on CD. Likewise the other way round - new music 'remastered' for vinyl.
Not all that helpful sorry but I think you know it is a thorny issue.