SurveyMonkey lawyers ask PopSurvey to stop using monkeys in ads. Yes, really.

I think that sometimes these things can be done in bad taste but I don't necessarily see anything illegal or unethical about it. Its pretty normal for a competitor to try to contrast themselves with a dominant company. Doing so can often lift you up to the level of the dominant competitor in the eyes of consumers and other times it looks like you're taking unfair cheap shots at the big guy. In this case I thought what Pop Survey did was okay. They definitely made their case by showing the difference between the products. I thought it was fair. Its not like they only went out name calling, they backed up their claim.