Karl Boehm is THE Mozart conductor. His symphonies are the best, his "Figaro" is the best, and--as you would expect--his "Eine Kleine Nachtmusik" is the best. Of course, Boehm has the greatest orchestras in the world to work with: the Vienna and Berlin Philharmonic Orchestras.
"Eine Kleine Nachtmusik" is taken at a slower pace than you will usually hear, and is heavier than Sir Neville Marriner's beautiful version with his Academy of St. Martin-in-the-Fields. But the patient tempi allow Boehm to display all the subtle musical touches of this often hackneyed piece, making it anything but background music. The VPO strings are appropriately lighter than the BPO's, so it's good that they take this serenade. But the rest of the pieces are performed with the BPO, and Boehm is able to get much deeper into the music than Karajan would on such Mozart works.
The "Posthorn" is so good it's scary. Levine's or Szell's versions don't even come close to the depth and beauty that Boehm gives us. Please don't play this work while you're studying or washing dishes!
The "Serenata notturna" is perhaps more successful in the hands of Marriner, but it's good to hear this little work given the big BPO treatment.
All in all, if you're looking for an "Eine Kleine Nachtmusik," this is the one for you--and you'll get to know these other equally great works. (Amazon)
Serenade No.13 in G major, K525 "Eine kleine Nachtmusik'