I also seem to have a few versions of the Planets. For Decca, at least on vinyl, with the Planets I prefer Mehta SLX2569 from 1971 over the Karajan SLX2305 from 1962 for sound quality. I also have Solti Decca SLX 6113, that is pretty good. I have Previn on EMI ASD3002 which is a great recording that is on the Absolute Sound HP Super Disk list. For performance I still prefer the Boult ASD2310 overall, that Walton lists above, and my copy is a good pressing.
As Stunsworth says anything on Decca from the 1960's (to early 70's) are usually superbly recorded, but many mint originals on vinyl are really high prices now.
Another Decca I would particularly pick out for both supberb performance and sound is Britten's War Requiem SLX Set 252/3 1963 conducted by Britten. This can still be found quite cheaply on vinyl.