If CR7 leaves Real this summer, I think The Premier League is the most likely destination. He is too much of a commercial superstar to go to China since he is going to be loosing a lot of image rights contracts that he will be getting if he is competing in a top league.
And the MLS might pose the same problem. CR7 is a superstar and he should be competing in a top league as he is still one of the best two players around.
If he is adamant about leaving Spain, The Premier League is the best choice for him and Germany or Italy come afterwards, but surely not as likely. So Manchester United is surely a huge possibility, but let's not discount other big English clubs or the likes of Juve and Bayern.
I personally would love to see him play somewhere else, just to see him adapt to new teammates and systems. And I'd also like to see Real do it without him. With Isco, Bale, Morata and a probable incoming future superstar like M'bape, this shouldn't be too much of a problem. I would like to see Benzema move on as well, preferably to The Premier League. If Morata stays I want him to play or move on to a club where he would be getting the first team football he deserves.