I find the XR-18 to be a little more advanced in terms of features. For remote control, it is compatible across pretty much all platforms. You can do full multitrack recording/playback via USB with the XR-18. More fx sends and more features/options. Good sounding preamps. Drop-box format is cool for strategic location and minimizing cable runs. Hard wired via standard networking cable to a router or computer/laptop is nice. XLR aux bus outputs a plus. If you're into discrete IEM mixes, the Behringer interfaces seamlessly via existing Ultranet components. The controller software/apps take a little bit of practice to get used to (could be improved IMO), but they seem to work fine.
The Mackie is a nice little setup, too, IMO. Depending on what you are doing, you may find some of its differences either a bonus or a non-starter. First, you have to be using an Apple device to control it. No andriod, no Windows. Docking an iPad is a good feature, though, for more "traditional" mixing. There is no option to otherwise hard-wire a remote control interface, though. I find the control software app to be pretty easy, intuitive, and well developed. Also good sounding preamps. Recording features and echo/reverb effects very limited, but functional IMO.
If you're looking to upgrade to a digital board and already own an iPad, then the DL1608 is a good way to go b/c IMO it has a "simpler feel" to the design overall - even though there is still a ton of dynamic, tone, and routing control available. The XR-18 allows you to go a bit deeper down the digital mixing rabbit hole IMO, and gives you a lot more control option possibilities, though you may find the control software a little on the clunky side. It is also a better choice if you're planning on growing beyond just the basics of digital mixing on a smart phone or tablet. You really can make this a viable center-piece of a home studio and/or rehearsal space. Not so much with the Mackie.
After I got my XR-18, I had planned on selling the DL1608, but didn't. I find that the simplicity of setup and operation was very appealing for some small shows, with the iPad docked (making for worry free operation). But if I'm doing something a bit more demanding, or recording, the XR-18 is the easy winner.
JMHO, YMMV.