Apex owner here. Have been a Neptune customer since 1999. I did take a break for a bit and picked up a Reef Angel but with the recent upgrade picked up an Apex. I still use the RA because it does some things just better than any other controller on the market (custom libraries) but the Apex is the primary.
Now let me remove my Apex and Neptune (bias) hat and just say this.
Ask yourself what is it you want in a controller. Seriously, it is that easy.
Now you can start to narrow it down to features, "known" product road map, etc. For example let us say you want automated water testing. If so then today that just leaves the Neptune. Down the road it will open up GHL but the ION isn't ready yet. See what I did? If you can wait it out then you can choose between the two product features. Now if you want automated testing but don't really care for a controller then maybe the Reefbot is for you. Pick up that, throw in a Seneye for out of water alert email notification, and Bob's your uncle.
We can continue to play this game but at the end of the day what do you want. Apex and GHL are probably the two big players right now that can give you reach back technology for alerting. Apex may go a step further due to the smart energy bar but as I said I do not own a GHL so maybe read up on
@Ditto 's thread for more GHL information. Those are the two I would look at especially if you want automated testing.
Open source Reef Angel is the best. Great community. Awesome custom libraries like geo location, full on clock cycle tides, weather with random day of week, month, and more. However, it is open source and you need some basic coding skills or willing to learn. Boolean logic, etc.
Hydro was mentioned. Has so me potential. Integrates with ecotech I believe. Lots of stuff if you search but again I can't speak for it. However, no automated water testing like the RA above. If you don't care about it than any of these 4 will work and you are back to feature sets.
To buy? Depends. Controllers will not save your tank if they are setup incorrectly just as they can save it when setup properly. They can also nag you to no end if things are not set up such that you filter or ignore. So to buy? Sure. It is a awesome product and they have a pretty solid foundation and user base. However, there are other options which brings us back to that bloody list I spoke about at the beginning