they all do pretty much the same thing so pick something cheap or even free.... seo sounds very difficult but it is not that bad....Just a few basic things to remember...

1. Keywords
-In meta title
-In meta description
-In website content
-in URL
2. Backlinks
-using those same keywords as anchor text

Not too bad?

I am over-exaggerating the simplicity, but you get the picture.

this really depends on your budget some cost monthly fees some are 1 time fees please share your budget so we can let you know what we think is best

I'd recommend SEO Powersuite. It's about the most complete toolset I was able to find.
Does keyword research, onpage, helps you get backlinks, tracks keywords, builds graphs and reports if you need it. You can try it for free before you purchase it.
But it'd be nice if you specified what kind of tools you are looking for. Cause we don't know what SEO techniques you practice, and the choice of tools would largely depend on that...

It really depends on what you are trying to do. If you are new to SEO, I think you should learn what SEO is and then come up with a plan, as there are a lot of ways to make your site popular in the eyes of search engines. Try one or two different strategies first. If those don't work, try another until you find one that works.