I think it'll be closer just because it has the perfect recipe of a close fight. Ortiz is young, hungry, southpaw, in his prime, champion, stronger, bigger, more powerful, and Mayweather is older, has been inactive, most likely expecting an easy fight (though im not saying he isn't training hard just like for any fight), and smaller.
I hate to do this but I have to discredit Floyds recent opposition,
1. Mosley was older, although bigger and stronger and hungry, older and out of his prime, and even though he came off a win against Margs, everyone knew he had this massive stamina problem and struggled against Cotto and Collazzo. Ortiz wont get tired that fast. Mosley had a good chance the first four rounds, but as expected he got tired and gave up the rest of the fight. Ortiz won't give up (I probably left myself open to a Maidana remark here, but Maidana's much stronger than Floyd and Ortiz just wasn't quite there yet when they fought).
2. Marquez was older, smaller, weaker, slower, even though he was hungry, theres just no way he was going to beat a bigger, faster, overweight Mayweather. No matter how smart he is.
3. Hatton was hungry, but slower, he looked to be stronger than mayweather, but wasn't, and had massive defensive flaws (actually, this sounds like Ortiz), but difference here is Ortiz is much stronger and bigger than hatton, Ortiz can take a punch, Ortiz is southpaw which is at least a slight advantage, and believe it or not I think Ortiz has better defense than hatton who would run in with hands under his chin, and Ortiz has much better stance and foot movement than Hatton who fought on the back of his feet rather than the toes.
4. & 5. Baldomir and De La Hoya - nuff said.
Ortiz has steady been beating better opposition each fight (Draw with Peterson was controversial and I think Victor took that as a learning experience, plus he brutalized Peterson for a bit there and made him dig for gold to pull out that late surge to earn him a draw), getting better each time out, taken bombs from big punchers and hasn't been ko'd (at least not from any single punch), and should be a little bit better in this fight than his last.
I might just be talkin a bunch of bull because I want Ortiz to win, but some things on here you have to agree with even if you are a Mayweather fan.
It'll be lopsided in Floyd's favor. But not discounting Victor Ortiz, it's just that Floyd is unmatched in the sport. He makes everyone look bad, or amateur.