Market Niches Software

Finding and selecting market niches

[Macbeth]

I've seen various software packages that claim to "assist" in the process of researching market niches on the net.

Could someone perhaps share their experience/opinion/relative advantages on the following packages?

Nichefinder
Adwords Analyzer
Wordtracker
other software?

I have trouble in that:

-I don't know which one to buy if not all of them

-Whether they actually work

Cheers

Macbeth