Opinions about Mullard El-37 Vs. Amperex El-34 DD

Curious from those that have heard both these tubes what their opinions are of the strengths and how they compare to each other. My amp can take both - though currently running Tung Sol 6550 BPs - and have the Amperex here while just buying the Mullard El-37. I hear they were one of the few tubes DESIGNED for audio use (El-37) so that has me sort of excited.
From what I know, the Mullard EL-34 is the best, way beyond the Amperex and the EL-37 is even better! I'd love to try the EL-37-where did you find them? In my book, the decision is a "no brainer" if you have the money.