Hey There,
I think they all have there places, but I'm sure you will here a lot of things good & bad about all of them. But the main thing is what are you wanting to accomplish. Are you more into PPC or are you looking for SEO.
I personally use Market Samurai which is great for SEO, and the support is pretty good. Right now it's still in beta form, and always updating it's very nice! Has a lot of features! (almost overwhelming)..
Some more that I've used:
Keyword Elite: It's geared more for PPC. I liked it but I liked MS better!
Traffic Travis: Kinda in the middle of the road of PPC, SEO! Not bad!
Those are probably three of the better one's! But I still use google's keyword tool quite a bit. Why not, get it straight from the source. That's where the rest get there info anyway...
Hope this helps!
