I made the switch from standard Tortex picks to the Eric Johnson Jazz III signature about 10 years ago because I preferred the shape.
Before long I realised that the compact dimensions, thickness and material of Jazz IIIs also produce a warmer tone with a very defined attack. I have not played a traditional-shaped pick since.
While the original Jazz III design was pretty much entirely satisfactory for me to begin with, the Ultex Jazz IIIs boast an even fuller, richer tone, in addition to being more durable and comfortable. While grip was never an issue with the Jazz III models, the ultex material really does wonders in helping you maintain control in even the sweatiest of scenarios :).
All in all Jazz IIIs have given me one less thing to worry about in the tone-chasing game and unlike a lot of the tonal trade-offs each of us has had to deal with, they actually make playing easier and more comfortable in addition to sounding good. I don't think I'll be using anything else in the foreseeable future!