The fact that the poll is 50/50 and we're on a site of a team whose fans adore him is another clue of who is the best betweent them. I don't even imagine how the poll would look on a Barca forum, also on every neutral forum or on a poll asking neutral fans we all know the answer, and by some distance.
Also almost all former great players (and active) all say that Messi is the better of them two, if not the best in history. Of course there is alot of revisionism going through given the fact that Messi is somewhat declining (by his standards, even though he won the double with Barca and the golden boot).
Ronaldo currently has a very good team around him that delivers even when he is absent, this doesn't happen for Messi on a club and national level where he is the focus and the driving force behind both teams. If you look at this season, Ronaldo from the home game against Juventus and onwards he was pretty absent by his standard, and even then his team won the UCL (Modric, Casemiro, Kroos is the best midfield in the world and the fullbacks are in top 3, the keeper aswell). Messi has one off game against Roma and his team goes out. The same happens at the national team (see the Euro final).
If we are talking about individual skill, Messi is always streets ahead of him, not only his goalscoring record is comparable to Ronaldo's even though Ronaldo is a striker, his playmaking abilities are from another world when compared with the portuguese.