What is the best sounding Mahler symphony cycle?

Here's a real sleeper recommendation for no. 4.

On the shelf I have Bernstein, Fischer, Maazel, Mengelberg, Salonen, and Szell, but I always return to Franz Welser-Most.  In particular, Felicity Lott floats the soprano part in the fourth movement more beautifully/ethereally than any other recording I've heard.