The Mule will give you more of a traditional PAF tone. The Crawler is a good all around pickup, especially if you're doing any coil splitting.
In a post from early last year, Tim compared the the Crawler to the Mule, saying the Crawler has "more power but similar vibe", being "fatter and a touch brighter with unpolished Alnico V magnets" (the Mules can be IV or II).
The Crawler is in many respects quite similar to the Abraxas (in sets, they have the same neck pup wind), though the bridge Abraxas is slightly more genuinely a "Mule+" than the Crawler. But IMO the Crawler is very versatile: a good middle ground between the vintage PAF tone of the Mule and the somewhat hotter "metal" Alnico pups like the Holydiver and the Nailbomb.
And the Crawler/Abraxas neck is
smokin'! 8)