For me, it's three factors: cost, ease of use, and support. Cost is an easy one. For anything comparable from other manufacturers, you're going to pay considerably more. Not just for the PLC system itself, but for the software to program it. Ease of use. The software is easy to install, easy to understand, and it allows not just me, but anyone who would need service the system the ability to look at the program. In programming, the instructions are generally streamlined and easy to understand and use. You can generally get what you want done in a minimal amount of rungs. Support. Obviously typing this here means we all know how great the support is. I undertook my first "major" project of my own late last year. I had a few newbie problems. I made a thread, and the Host staff (as well as other experienced users) helped guide me through my errors. That's almost invaluable. Being able to get online, post about your problem, and then have it answered within a short timeframe is huge. Not only does the problem get solved, usually someone comes up with a sleeker solution to your operation that you would've never dreamed of. That kind of support is a major reason I use the platform in any application I can.