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Neither tank is really suitable. Though you could have a pair in the 29 (see below though).
These fish don't mix well with others, or each other.
If you get two males, one will die.
If you get a male and female, they will kill other fish.
If you get a male and female, they WILL breed and overrun you.
Convicts can be aggressive, as I said above. I've had single convicts in with other fish, but not in anything as small as a 29. They are territorial and I honestly think they'd (eventually) kill anything else which would fit in there with them and didn't give them their territory, they get quite big...