Banana rum is usually pretty crappy as far as rums go. Usually overly sweet and with artificial banana flavors, this stuff is meant for the frat house punch bowl or the chain restaurant's "Daiquiri".
If you do want to get some banana rum though a serviceable brand is Cruzan Banana Rum. It is stronger than the usually weak stuff you will normally find in the aisles of your liquor store. When sifting through cheap cordials or flavored rums or vodkas, one rule of thumb is the stronger choices are usually drier, not as overly sweet, and hopefully a better choice. Such is the case with Cruzan.