As a general rule: Champ/Z/Opto style plastic is the most overstable, Star/ESP/Gold Line style the next, then Pro/X style, then DX/D as the least. The speed in which they break in follows that same general rule.
It's important to note however, that different discs cool differently in different plastics so exceptions can skew that general rule thanks to really high/low PLH, dome, flashing and other characteristics. A lot of the older molds that were designed before premium plastic can be markedly different and arguably fly better or truer in base plastic. The Cyclone is a good example of this, Z Cyclones didn't mold up much like a Cyclone and are generally regarded as glideless junk.
How do I use this knowledge?: A lot of base plastic discs are great for cycling, i.e. having multiple discs of the same mold in different stages of wear (read: stability). Say you really like the Eagle or Teebird. You can grab 3-4 and start beating one into an understable disc, then eventually you have all stabilities covered from fresh (overstable) to beat to hell (understable). Same mold means more familiarity which breeds consistency.
The other route and probably more common one is to pick up discs that fly "out of the box" like you want and will stay that way due to the premium plastic. The only big disadvantage of this is if you lose that perfectly flippy Champ Leopard, it can be a task replacing it with a similarly flippy Champ Leo, plus premium plastic costs more. But, even if you're a cycler, it makes sense to fill those really overstable slots with premium plastic discs because even DX Firebirds or Banshees will lose that dependable overstability eventually.
Because all discs regardless of plastic will wear in at least a little bit, what I like to do is get a premium plastic disc that is a little bit more overstable than what I want when new because it'll beat in to a point and stay there for a very long time. Finding a mold that beats into the sweet spot of stability you're looking for is simply great and you'll get a lot of use out of that disc.