I'd definitely have Mancini. I think he bought well at City and has plenty of experience of winning as both a player and manager. He totally transformed City, took them to Old Trafford and won 6-1, ended up winning a championship with a last minute goal in the last game of the season, preventing their arch rivals to the championship.
He oversaw the end of the 'Typical City' ingrained negativity that was once prevalent at City, and is now prevalent at Everton with this horrendous 'Everton that' saying that is used whenever we fall on our arse. I'd like him to oversee a similar revolution at Everton.
The problem is that he isn't out of contract until next year I think, so we would have to pay compensation in the event that we could actually attract him. He is also being linked with a small club from North London:
http://www.express.co.uk/sport/football/658288/Roberto-Mancini-quit-job-Arsene-Wenger-Arsenal-axe
That's why I think Pellegrini is far more realistic. He will be out of contract, available and living down the road
at exactly the same time that we will sack Martinez. No compensation will be needed.