If you are involved in search engine optimisation you must use SEO tools!
SEO tools are absolutely fundamental for any SEO professional. Whether it be browser tools, back linking tools, article spinning, link finding, competitor analysis etc etc.
If you're looking for the right SEO tools that you need to think about which area of SEO you want the tools to help you in?
For instance if you're an SEO agency you will need help around client management and reporting much like a CRM system.
If you're just doing SEO for 1 to clients then you'll need tools to help perform SEO tasks such as content writing link building and possibly even automated website development.
There are tools that cross both boundaries and not only help with client management, invoice generation/payments but also do lots of the SEO tasks that any SEO professional will need to do on a regular basis.
If you have multiple clients is best to first of all look at the high-level SEO tools and see what they have to offer. What you're looking for here is CRM management but also SEO work flow, planning, implementation, outsourcing SEO jobs, content development/writing, back linking, keyword position monitoring etc etc.
The great advantage of using high-level SEO tools is the automated reporting elements to keep clients happy that your working for them each month trying to get them to number one in Google for their keywords. Different SEO tools have different approaches to reporting the most up with some giving the client a URL to visit, while others output PDF which is e-mail to the client each month automatically.
Whatever is your preference SEO tools for the SEO professional are a must it is worth your time to do the research and due diligence looking at every SEO tool on the market and deciding which one is best for you. You will probably find yourself using to maybe even three SEO tools especially when it comes to some of the SEO tasks that need to be done each month.