The absolute best catfish cleaners for Malawi Cichlids are Synodontis catfish. They are a little pricey, but keep the place clean. I have a johanni cichlid that is insanely territorial, and will only let the catfish com into his little alcove.
The bigger your cichlids, the bigger the synodontis, they're about $13 for a 2'
If you can get away with that, do so. Butif you need bigger, you'll have to stretch out that wallet a bit.
Synodontis will get around a foot long, but blend in very well without disturbing the beautiful veiw of the cichlids.