Which algae eater would you recommend for a 20g tank (living with tetra, platy and cories)?
Otocinclus, Bristle nose catfish or Siamese algae eater?
If otos, how many is the minimum?
Ottos are the best thing for a tank that small. Everything else will likely grow too big and strain your tank. Heck, they will likely clean the tank the best as well.
A small group is best. 3-4 will probably suffice. Remember not to overstock the tank though.
Overstocking is one of my concern. Do you think that if I only get 2, they could still be happy?
I also eared about a 1 otos per 10g rule, which would make 2 a good number.