In the Rifts RPG, does a character with the Crazy O.C.C receive the benefit of all five super-senses listed, or do they have to pick one?
All 5 of the crazy's senses are heightened
Although slightly unclear in the Rifts Ultimate Edition (2010 4th printing), the crazy O.C.C. does, in fact, end up with all the enhanced senses (55). No mention's made of the necessity of picking but one.
By way of comparison, earlier Rifts editions had different layouts for the crazy O.C.C. yet identical (or nearly so) effects. For example, the layout of Rifts (1990) has the O.C.C. gaining as #4 instead Heightened reflexes, agility, and senses (56), that section going on to list the effects of all three abilities and making no mention of needing to pick between the three.
Finally, Mindwerks (July 1994) describes assorted physical M.O.M. augmentations that essentially permit custom crazies (if the dude's willing to submit to surgical experiments conducted by (I kid you not) the Angel of Death1). Among these M.O.M. augmentations is hyper sense, an implant that "enhances the five senses and makes the character very alert" (20). In the crazy material I've seen,2 there is no option for getting an M.O.M. implant that heightens only one sense.
1 Not an actual angel.
2 And I've seen a lot. After all, I read Rifts books. Thank you. I'll be here all week.