Which Would Make The Bigger Mess

[Big_eyes]

Which would have a smaller waste footprint on the average tank?

 

[Mr Spoon]

IMO I would say a small pleco because they don't stay small for long and are poop machines.

 

[Truck]

Without knowing the size of the pleco I'm unsure, but I think the Oto's would produce more waste.

 

[Big_eyes]

Was just thinking of something like a bristlenose plec or similar that doesn't really grow mahoosive.

 

[Truck]

I'd say ottos

 

[hamfist]

Depends hugely on exactly what kind of Plec. Some plecs eat a lot of green matter , and even wood, and can produce enormous amounts of poop. For an adult Bristlenose, though, i suspect that 10 oto's would produce less waste.
However, a small omnivorous Hypancistrus-type of Pleco would probably produce less waste than 10 Oto's.