I own two JL Audio F113 mk2. Properly tuned they sound really great with the XLF - I posted about it in the past. More recently I got a single Wilson WatchDog passive subwoofer, a Wilson Watch controller (active crossover with phase, level and a variable frequecny and Q parametric equalizer) and a Theta Dreadnaught amplifier. Used with the XLF, the Wislon Watchdog sounds better to my ears and a few friends ears than the JL Audios - it blends better with the mains.
I know subwoofers are not made to be tapped with the finger knots. But if I tap the JLAudio I listen something like a boxy "pock, pock" . If I tap the Wilson Watchdog I get a more dry "peck, peck" sound. The JLAudio is a closed box subwoofer , the Wilson is a vented subwoofer, like the XLF. Probably these are some of the reasons why I prefer the Wilson Watchdog.