I moved this topic, as it's not really about "South American catfish (other families)".
The actual question(s) aare hard to answer, because it depends on what you mean by "best"...
Best looking, schooling one would be
- but that's not the same as "best at cleaning up" - not sure what I would put there, perhaps
(not that they're ugly or anything like that).
Non-schooling, again, depends on what you want it to clean up first of all, and second how you define "best" - I'm not sure I can write down a single one - although
are always high on my list - but perhaps that's not properly a scavenger, as they are better at eating algae than other stuff (although given a chance they will eat many other food-items too). Any
would also be a good Scavenger, simply because they eat just about anything (but not very good with algae-growth, so if you have algae-growth in the tank to get rid of, you'll need something else too.
are nice to look at and falls into both categories (can be kept alone, but better in a group of 5 or so).
However, besides from the discussion of which is "best", there's obviously some other fish that you like to keep with these, which will be another factor (along with the conditions of the tank - temperature for example, planted or not, filtration/oxygenation/water movement in the tank, etc, etc).
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Mats