I've tried both the Polycraft FC6600 Slow Set and the Polycraft Opti-Cast 100. Both are water clear and work well. The resulting casts are very similar - the main differences between them is the pot life. I will say that the resin blanks are very difficult to polish, but I understand that this is the same with Alumilite clear (I've never used it, so I can't directly compare). I always use a vacuum chamber when casting, but not a pressure pot, so I'm not sure what results would be like if done differently.
I've also tried Polytek EasyFlo Clear. It's an amber transparent resin. Again, it produces a nice blank, in fact I prefer it to the two above, as it polishes up much better and easier. The issues with it are obviously the colour cast, but also the fact that it has LOADS of air bubbles. You definitely need to use a vacuum chamber or pressure pot - however, it only has something like a 2 minute pot life, so you don't get much time to mix and degas (I can just about manage it when doing a one colour cast, I wouldn't want to attempt it with 2 colours).
