There are some good comparisons on RF; here is just one example.
http://www.reefcentral.com/forums/sh....php?t=2184396
I recently acquired an Apex, and can see no limit of things I can do with it, from ATO, flood prevention, etc, etc. I think that is its big advantage, being able to add modules and program it to do almost anything you want. I haven't researched the Reef Angel, but understand it is not as comprehensive and expandable.
But am curious about what you are looking for with wifi communication to your iPhone. With the Apex, it is connected to your home network and internet through your router, so works with anything that is connected to the internet and your router (incl wifi to your iPhone) . Also you can add wireless connectivity between your Apex and your router (just don't use it for firmware upgrades). Of course I am assuming you have a wifi router (who doesn't?).