Easy
My would be the one...the only...S&W 686. I recently inherited my dad's 686 no-dash, and I can't imagine a better wheelgun. I noticed a few Python lovers, and while I've never fired or own one, I've got to imagine that the 686 delivers the same quality, strength, and accuracy (if not better) than the $1200-$2000 priced Python.
If I were to have only one .38 (that is to say, not capable of fireing 357's), it would be my Colt Official Police. A little heavy on the trigger when compared to the 686, but boy oh boy is it fun to shoot!