I would say gold saum. As for the growth, these are one of the slowest growing fish I have ever kept. However, at that small a size, you should be putting on about 1/4 to 1/2 inch a month until they are about 5 inches.
I would suggest trying a different food. For a fish that size, try some NLS, or the HBH Super Soft with Krill food. That should help with growth.