I think one of the reasons most clubs don't want Ronaldo is as said, due to his age and experience. He is past his peak performance and can only be of much use in leagues with less stress, unlike the English premiership. Also, with the vast experience he has garnered over the years, he might be too heady or superior to the managers or team members. It is also likely that if Ronaldo is in a team, the game is kind of bound to be centered about him. Managers know this, and dont want an influence bigger than theirs. If I were him, either I go to the Spanish league or to the American league because he still has to remain fresh for Portugal in their oncoming world cup campaign.
If Ronaldo want to play in Spanish league, he will only prefer La Liga Santander which is where the club (Real Madrid) that he was before he went to Juventus, then back to Manchester United. With how he is in Manchester United now, do you think coins like Real Madrid, Barcelona can prefer C. Ronaldo to play with them again? He is getting old in football and that may not be possible. The best is for him to later join MLS is what I can think, but I do not think it is now he should join.