I tend to be a bit, ummm, brutally un-romantic & crusaderly anti-mojoistic? And, though this may date me (cheap date!) I started making my own picks just shortly before Dunlop came out with Tortex & the first, small red Jazz III's - 1980 or so. And, I spent a whole lot more time than strictly necessary learning about all SORTS of different plastics, more when I was making my own (plastic!) steel guitar bars.
Believe it or not, there really ain't a whole lot of top-secret, arcane, lost-mysteries-of-the-ancient-Mojo-Gods kind of knowledge about plastics - there is, like, strength, and hardness, and slipperiness, and thickness, and shape. Over the decades I have made just about every shape imaginable, yes 3mm thick tri-corners with three different points, yes holey, groovy, contoured etc. The Clayton ultem/Dunlop Ultex picks go about as far towards hardness as I want to go, short of stainless steel (I made them too). And the nylon is about as far as I want to go towards softness. Dunlop's red nylon is hardened-up with the addition of silica to make their harder black ones - AKA powdered glass, sand etc. As I'd bet a donut that delrin w/added silica is the secret formula of Dunlop's "Tortex" & the Planet Waves picks, which are Dunlops, but in different thicknesses. (Dunlop, Pickboy, and Clayton make a good 95% of the picks in America.) D'Andrea makes a few sizes of celluloid picks I've never seen elsewhere, so maybe them too.
I alternately use Clayton's "acetal" picks, D'Andrea celluloid picks, and Dunlop nylon and Clayton/Dunlop ultem picks. There's no material I've ever tried that does everything better than one or another of those - as should be obvious, it's all about different trade-offs. Too heavy/thick makes for a lot of clicking, not a problem on zero-gain-staged bluegrass guitars or most applications of electric bass, but when you start piling on gain stages the clickiness ramps up quick - which some metal guys LIKE, but not me. I do like to put HANDLES on picks with Milliput, a casting epoxy:
The ultem picks are so hard that they transmit handle weight, adding more clicky noise, but I can still find some use for a relatively thin 0.96mm ultem pick, made with the round shoulder as the playing surface, with a Milliput handle. And the nylon and acetal picks work great with handles, and there's a lot that can be done with the taper of the point(s) and the fact that you can make the tip a bit flexy but with a totally rigid handle. Celluloid is the softest, they will notch up, but they also can go pretty thick with no click, ideal for recording perhaps. There's all sorts of interactions between hardness, click, thickness & point shape - suffice it to say that I can get some sort of decent behavior out of anything between about 0.96mm and 2.0mm or so. I personally don't have a reason to ever go thicker - there's no material difference in the flex among ultem picks once you get past about 1.5mm - but it can be comfy to grip a big fat and grooved 3mm handle, just not for the strings.
If your Milliput stash has run low, you can do a quick 'n' dirty handle with silicon tub caulk, skateboard grip tape, or just GLUE three picks together for the handle but with a mono-layered point; drill holes! In all cases, drilling holes lets the two sides of handles cozy up. As several manufacturer's have noted, putting two or three different-shaped points on one pick can lead to some hilarity. And, it's cheaper than collecting Ferraris.
