Which of Mozart's No.39 & 41 CD should I get?

Performance wise, I don't think you would be disappointed with Josef Krip's. But it the recording might sound a bit outdated.

Kal...I have several recordings of these old war horses, but your strong endorsement of the Mackerras interests me. I also listened to the brief clips on the web site.
Please elaborate regarding your suggestion.

The earlier Mackerras on Telarc is a good example (to my ear) of a Telarc recording that was less satisfactory. The string sound is (to me) a bit edgy, which is annoying given that the strings are the name of the game. However, Mackerras is a good Mozart conductor, and I just ordered the Linn set myself last week. It should be excellent. And Symphony 40 is a "must-have"--one of the great works in the "canon."

A very nice budget set by is by Saraste on Virgin, which has several other Mozart Symphonies (though not 40). Lesser known conductor, but I liked this set.

George Szell and Bruno Walter were (for me) two of the great Mozart conductors, but their Mozart symphonies seem to be kind of hard to find now. The Walter set of late Mozart symphonies is available from Arkiv Music, but the Szell is only available is a big boxed set. And the recordings are a little bright (though tame-able, if you have tone controls).

If you like the symphonies, the next stop should be the late piano concertos. Many fine recordings...

http://stereophile.com/musicintheround/508mitr/index1.html

Another variation is the Hogwood/Academy of Ancient Music "The Symphonies Vol.VI Paris & Vienna" on Decca (L'Oiseau-Lyre 421 085-2). It's an old recording from 20 years ago. What's striking about this is a smaller classical orchestra with period instruments giving the symphonies a slightly smaller sound - almost like a chamber orchestra - that the jacket says is what Mozart had intended. Good recording quality for the time and, I think, a very good interpretation with top notch musicians.