I will suggest a few humbucking/humcancelling pickups that I've tried in my fretless Geckos:
Carvin "H50A" (or "H50AS" for the P2 shape soapbar model). Great clarity and warmth, and a very nicely focused tone which sounds like a nice single coil. The fundamentals are a bit thin for a bridge pickup, but the sweetness of tone makes up for it. These work well in any of the 3 Gecko pickup positions: bridge, sweet spot, or neck. I would pair these with a midrange-rich fingerboard wood such as Bubinga to get the most growl.
SGD Neodymium ND3 soapbars. These are not quite as bright as the Carvins, but there is a very good balance of tone across the frequencies, and the fundamental tracks very nicely. They do sound more like a humbucker than a single-coil, but when paired with a nice bright fingerboard wood (e.g. Ebony) the natural tone is unmatched. The midrange is very usable and works well with a fretless.
Villex "classic" series pickups, available as "split coil" J-shape or soapbars (custom order). Excellent grip on the fundamentals in any location, especially the bridge position. They have a rich, warm and very detailed midrange which brings out the nuances of the woods, and can growl to some extent. These have a very broad frequency response, and work well with any fingerboard wood.
My experience with Bartolini and Delano J-shaped pickups is rather limited. Their dual-coil humbuckers are nice, but probably not what you are looking for.
Q-Tuners are getting to be as rare as hen's teeth. If/when the shop ever starts production again, I'll be one of the first in line to buy another set. In the meantime, there are many great pickups out there.
