Ok let me go in to more of what I have used.
Keyword elite, total crap in my opinion. give so much crap results if you use anything beside the free google tool and wordtracker tool in it.
Market Samurai, pretty good software, but extremely slow if you handle anything over say 1000 keywords not to mention that if you do more than 200 keywords at a time it will usually get you an temporary google block on their search.
Wordze.com pretty nice actually, but still was not to satisfactory in my opinion.
Wordtracker.com payed service, also not good enough nor does it give enough results in my opinion.
Google tool, very relevant keywords but also the same keywords that everyone else are trying to target. and to few results.
Seodigger, was an excellent service, but they closed down and now offer only semrush. semrush is suppose to come up to the same level as seodigger so I see great big future for it.
Semrush and Seodigger work this way that they have a was keyword list and they have checked all this keywords agains google, and continue to do so all the time and see what pages ranks for them.
So you can take a link or an url and check what this link is ranking for.
That you could do in Seodigger, but in semrush they only give you what the whole domain ranks for now.
But what is great with the way they work is that in semrush I can f.ex. type blue widgets and I will get a keyword list for bluewidget by them going and getting other keywords that this specific pages that ranked for blue widgets also ranked for, so this way I get highly relevant keyword lists.
Kandor