I've used LTP, UNF and MS, and - to reiterate what other's have said - would rank them that way in order of comprehensiveness... MS has a whole suite of other modules that the others do not (they are "purer" KW research tools). That being said, I've only ever really used MS' KW module, so I can't really speak to the effectiveness of the rest of them.
Agree that LT's competitiveness score is unique and helpful, but that's only available with a Platinum subscription.
And big-up's to Divok for recommending KeywordRevealer / Been playing around with it recently and think it's a great free alternative (though basic). Especially like the social signal data on the analysis page.