Actually all of them are going to be inaccurate if you are using them for traffic numbers. The best tool is still the Google Keyword Tool, but it's numbers are averaged over the last few months and then rounded. They have been know to grossly over and under estimate natural traffic many times over. Use any tool as a gauge of it's importance in relation to other keywords, not of exactly how much traffic you might get.
For long tail, if you can find it in a keyword tool, it's mid tail, not long tail. The good long tail traffic is received when you write on topics that are relevant to the end user, answer questions, etc. These are impossible to know via a tool, if you want to know for sure the best tactic is to ask your users. Surveys and just conversations are the best inspiration for content ideas.
