Ottos do much better on algae, hands down, no douts about it!
CAE will only eat algae when they are really young or very hungry. I have heard they get quite agressive when older too. I would NOT reccomend them to anyone.
SAE on the other hand are great. I have SAE and Ottos to take care of my algae and they do well. the Ottos are great on flat surfaces and leaves and the SAE are good for getting into cranys and the rocks.
Don't get the False SAE tho. They look much prityer than the real SAE but the false are muchmuch more agressive (only to other bottom feeders tho.) They defend their territory fearcly.
The article from the Krib is the BEST! I love it...printed it off a few times over the years and gave a copy away.
As to vulnerable, the Ottos are a bit sencitive to amonia and nitrites. You need to make sure your tank is fully cycled befor getting these guys. You have to give them time to get aclimated to the water...no just dumping them straight in after purchasing! I have always had some of these guys and while I do lose one or two the day after bringing them home (due to stress or starvation at the pet shop) they last for years and years.
I hear they do much better in schools of 6 or more too, but I havent had a big enough tank to warent such a school so I dont know. I do know that my one solitary one is very skidish and likes to hide lots. He was more relaxed with other ottos in the tank so there could be truth to the schools idea.
I've heard people trying to keep Ottos in a tank with no reall plants and it always fails...but that should be a broblem if you are useing them for algae control.

But just thought I'd point it out...I hate seeing these poor guys shiped off to bear homes and starved by unknowing owners....