Greetings, newbie here.
As a Madrid and Man Utd fan, I'll go with Ronaldo if we are talking about their entire careers. He has certainly worked hard enough for almost two decades to compensate the advantage Messi has over him in the raw talent department.
His statistics and trophies are there to prove my point.
Messi has been missing from big matches for a couple years now, which is odd when you look how easily he used to score against Big 6 teams or Madrid in his early years.
The Copa America bit someone mentioned a couple pages back, well...That was basically a tough game against Brazil (in which Messi did nothing of note, and even missed a biggie) and a few skirmishes against B or C-tier teams. Not to mention they are hosting this tournament every 2 years now... Laughable.
As for now, Messi is a better all-around player while Ronaldo keeps being an elite finisher. And the quality of their everyday opposition will be quite different as well. I predict that in the next couple years we'll probably see Messi scoring 40 to 50 goals in the weak French league, and hype around Lionel will be at an all-time high. Brace yourselves for that one.
I hope Cristiano keeps up with Messi and bags us a couple trophies during this second era