Over the years, the trend has been from large/thin to small/thick. So the Jazz III shape is now my fave.
I tried different materials and kind of like to switch between the Jazz Tortex 1.14mm (warm, fat, silky, mid-bass) and the Stubby 3mm (warm, fat, but more crispy, trebly).
Next, I would like to try the Ultex thing and some carbon fiber stuff, and ear are they sound and feel.
For mellow rhythms, I've recently tried the dunlop 204s. Very different feel.
Picks are a cheap way to mess with your tone a bit and look for something different.