I spent some time looking at the different engines that are normally considered these days. (Unity, Unreal, Cryengine)

Unity seems to be great for cross-platform development and the creation of certain types of games. It is likely to be the most flexible. But, it's also extremely complicated, has poor documentation and has some weird ways it goes about doing stuff. (I'm not a code-monkey, I just read the opinions of others.)

Cryengine is beautiful and has some really nice rendering features. But, it also has some issues that a novice might not like and has some documentation issues and such. Unlike Unity, but very much like Unreal, it's more tuned towards First Person Shooters and such.

Unreal seems to have the best of all worlds, with the exception that it is also more finely tuned for FPS. But, it's also open-source and the source code is available to anyone who wants to take a stab at making it do something they want or even fixing bugs before the devs get to it. It's capabilities seem to be improving as far as versatility goes and its development seems to be much more active than either Unity/Cryengine.

Documentation for all these is a complaint, but Unreal seems to have a more active community and its open-source nature means that people, knowledgeable people, can take a look at the code if they have a question and, perhaps, help answer questions and squash bugs and even develope new tools or their own version of Unreal, with all the features they want. (And, put them up for sale for others, too!)

Unreal gets my vote, right now. It's cheap (FREE!) and doesn't require any convoluted licensing agreements. And, it's capabilities seem to be on par with Cryengine, as far as rendering is concerned. (If not at equal level, many claim that new features are on the way that will get it there.)

But, for cross-platform portability and flexibility, Unity is still the likely choice. But, it's very costly at certain levels, I think.