You can ask this same question 100 times and get 100 different answers. ;)

On this forum quite a few people are fans of Alaskan Fish Emulsion. I use it every now and then but I think the 5-1-1 balance is skewed towards nitrogen a bit too much and thus only really good at developing foliage.

My personal belief is that bananas should either just use a balanced ratio like 16-16-16 or 20-20-20 and that during the growing season you can use double the recommended amount though it is best to break-up feedings so that they occur weekly rather than monthly or biweekly to avoid "spikes". Certain varieties may be able to make better use of more of any one of the nutrients such as more nitrogen for really leafy varieties or more potassium for fruiting plants.

You can also take a look a this link. It has good info and multiple suggestions from various people:
http://www.bananas.org/wiki/Info:Fertilizer

Here is a link that might be useful: Banana Fertilizer Wiki