Beast 3 - just because it is the only one of the three that is actually playable without cheating.
If Beast 1 & 2 were arcade games, then fine. But games for home computers should not be put at such a level that you will never complete them without cheating. Very very hard, yes, but (nearly) impossible?
I did hear of a couple of people who completed the first two without cheating (on csag) - but I am not sure I believe them...