As for the top Messi season, I think it's really difficult. 2010-2011, 2011-2012, 2012-2013, and 2014-2015 were all so good. If I had to rank them, I suppose I'd say:
1. 2011-2012
2. 2014-2015
3. 2010-2011
And that's only because he got injured at the business end of 2012-2013. A great...