After running dozens of websites I still can't find a 100% accurate tool. On one of my sites the tool shows a phrase should get little to no hits but in reality it gets hundreds. I think they are good for mainstream words but maybe not the less obscure one. Try google estimator if you are going to use one though.
@GameFriends.com - I think the problem with density tools not being accurate is that search volumes fluctuate and so there can really only be a rough estimate.