The piezos which seem to get the most consistent praise are the RMCs (
http://www.rmcpickups.com). John Turner has them in a couple of his Conklins, and Jeff Rader has them in is new Nordstrand--I'm sure there are others.
I haven't played them yet, but I have a Curbow being built which will use the RMCs for both piezo/magnetic blend and for driving a 13-pin output for Roland V-bass and MIDI conversions. However, they are rather pricey compared to some of the other options out there.
Mike