Great question. The CORE is the most compact, easy to use, & easy to install system with more advanced electronics and sensors. Its control module, cell, and flow switch are all integrated into a single unit (which you can take apart easily for service or replacement). The RJ models have will give you lots of power and lifespan (the two most important things) for the money, and have long been a customer favorite. Its controller hangs on the wall, and it does have lots of different settings and diagnostics. Its cell and controller get installed independently in the plumbing. Let us know if you have more questions or just call for faster service.