ProfiLux lead the way in quality, reliability and the very highest of grade parts including pretty much bullet proof probes, but its the vast functionality everyone talks about and how market leading ProfiLux is with keeping up with reefing technology such as LED control and providing everythign an LED diyer would need to have full system control access from ProfiLux. This may not be important now, but in 3-5 years, we may be all switching over to LED lighting with the improvement in the technology and associated costs.
The other important part to highlight is the huge amount of third party control options that work with ProfiLux, multiple companies allowing Profilux access to their system control features and others that GHL have engineered dedicated control options for. (Ecotech, Tunze, Hydor, Wingo LED, Aquarium Illuminations, Pacific Sun LED, Reef Republic LED, Eheim, TMC with many more to follow). There control features are specific to the products and not a plug and program like all other controllers. For example, with Tunze, you can utilize all of the options that their controllers come with, built into the Profilux module. This saves on the necessity of a multicontroller for example.
The ProfiLux has a built in web server with it's own browser. They are the only controller that offers this. Additionally, it has the ability to integrate into house automation, I believe it is the only controller on the market with the connection standard, but in the end, it all comes down to software. It is also the only controller with an SMS module. If your power goes out, the system is dead, however the SMS unit is a complete separate entity with its own battery back up, so if power fails the unit will still be able to inform you. Many tank installers get these as an absolute must for the systems they install. It runs off any active GSM cell phone sim card.
With the multiple interfaces and expandibilty, if you are a serious hobbiest in it for the long haul, there really is no other option.