Honestly unfortunately unless you are resolved to use Final Cut and Final Cut only then none of the Mac's right now either iMac or Mac Pro would be good for a professional editing machine. They all have AMD GPU's which is just bloody awful. AMD GPU's although fast, for the most part have awful awful support throughout both photo and video industry application wise. The drivers are horrible, and you will have any combination issues/glitches/poor performance/crashes with almost any Pro app that isn't Final cut Pro. Visit the support forum of any pro app developer and you'll see what I'm talking about. The problem is the way AMD computes and what developers have to do to make applications that support it well and are optimized for it, it makes it very VERY difficult to develop for. So from an industry perspective if most of the Pro world is on Nvidia anyway (taking into account Windows and OS X) and Nvidia is much easier to develop for while maintaining stability and quality of your application, then why spend all the extra time and headache attempting to make AMD GPU's play nice? I have to wonder what is driving Apples decisions to release now all of their nice but very expensive devices with an inherent handicap for most of the users who will be using the high end models. It could be by design since they've spent a lot of time optimizing their Final Cut with AMD, then they'd rather sell a machine that works only best with their software and screw anyone who wants to use another vendors software. Not saying this is definitely their thinking, but it does seem like it. The unfortunate part is they don't even offer Pro Photo software anymore - so for Photo folks they are really getting screwed.
It's a long winded answer for sure but the short of it is, unless you are going to use Final Cut and ONLY Final Cut for video or pro work then none of the current Mac's out now would be a good choice. However if you are OK with a machine that is pretty good/great for Final Cut and kinda OK or meh for everything else then I would definitely get a 27" iMac with the AMD GPU's - the Intel isn't even an option when it comes to video editing. If you could afford it, I would choose the top of the line model with 16GB of RAM as it has the better GPU and CPU.