I had all three on my Road Worn Strat before I traded it away.
Out of the three, I like the JB the best, but I generally like it better on all guitars. It has a nice upper midrange emphasis that sits well with other stuff playing. It's chunky in the low mids, but the bottom end doesn't extend as deep as the other two. I wouldn't say it's loose because it's not bassy, but it is kinda squishy feeling because of the low mids and the soft-ish attack. The high-end is not particularly extended, but it doesn't feel dark because of the high mids. The mids are also voiced well for me, as it's cutting in the high mids, chunky in the low mids, but not vocal or nasal like many DiMarzios can be.
The Distortion is what you would expect if you took the JB recipee and dropped a little extra 80's Metal dust on it. It's has more output, but a high mid emphasis as well, but the actual top end is more extended and aggressive. The bottom-end is deeper because it shifts the low mids of the JB down. Although I wouldn't call it a bassy pickup, I do feel it is deeper-sounding than the JB. It does feel more immediate.
The Custom I just couldn't gel with, but I'll try to be as positive about it as I can. It also has some aggressive high mids, although I wouldn't say that's the focus of the pickup. It has extended highs similar to the Distortion, and the actual core mids are kinda scooped. The standout thing for me about the Custom is the bototm-end is super deep and rumbly. It's weighty for sure.
Now on to the subjective, I do feel the Custom is a tad too fat for me. People often find the JB "loose", but I've personally never felt it's "loose" so much as it is "squishy" and the attack isn't as immediate. Well, for me, the Custom was way fatter, and way more problematic in the lows. I love the high-end of the Custom. It comes off more as "detailed" rather than "aggressive" like the Distortion, although it does have a hint of aggression. However, that bottom-end just doesn't gel with me. On the other hand, I kinda get along with the JB better, but honestly, JB and Distortion are varying degrees of awesome and I might prefer one or the other under certain circumstances, but I know I can make both work most of the time.