Well, the Mule is basically like a late 50s Gibson PAF. PAFs weren't all the same, some had more windings than others, they used different types of Alnico magnets, DC resistance varied between 7 and 9K - but the Mule is around 8K, and about as near as you can get to a "typical" vintage humbucker tone.
The Crawler also has a PAF-like tone, but it has significantly higher output so it'll overdrive an amp more easily - but won't clean up quite as well. The Rebel Yell is similar in output to the Crawler, but it's brighter and tighter, with more emphasis on the upper midrange.
For maximum versatility the Mule is, by all accounts, the perfect choice. It'll do clean, it'll do dirty. It'll do pop, blues, indie, rock, even a bit of metal. If you want more of a classic rock/70s hard rock sound, go for the Crawler. If you want a rock sound with a brighter, more modern edge, go Rebel Yell. That's about all I can tell you really.