I have a JJ and love it but it doesn't get used much lately because it excels at travel I don't really do. Most of my cooks are at home, where a standard 18 makes more sense. The JJ requires a viable table of some kind too, and a way to hang the tongs. But I love having both since grates can swap. The bottom vent on my JJ continually becomes loose. And the nearly non-removable ash pan (it's a pain to remove IMO) is a joke, which is why many of us use a 8" pie pan on it. And a lever for the bottom vent made from a long bolt bolted to a hole you make in it ...
That said, MrHoss indirectly brings up an interesting argument against the standard 18 when he mentions grilling on the JJ. This may be a bit off topic but it's my impression the standard 18 never quite knows what it wants to be. It's typified as the better machine compared to the JJ due to its deeper bowl size/airflow.
But indirect cooking requires either distance or other strong division from heat and the standard 18 has neither. On a 22 indirect is easy because of how far apart you can separate heat from food. On the JJ, because everything is so close, you're forced to take stronger action by way of firebricks or something more inventive. But on my standard 18, firebricks either just soak up heat OR heat flows over onto the other side. But because a firebrick is much closer to the grate on a JJ the heat stays divided better, in my experience. You'll also see more creative cooks and uses out of a JJ on this site. The little dude is damn inspirational.