SEMrush is so feature rich it's like your most favorite desert and after dinner drink all in one - with second helpings included! The keyword data, the social posting tool, the competitor data and more is simply incredible. The training tools, special webinars, and all the support SEMrush offers clients is of tremendous value over and above all its functionality as an SEO/SEM tool.
SEMrush provides great insight into a prospect's pain areas, and where they might need help. It provides a data driven evaluation, that prospects appreciate when they see how their website is seen from the outside. I believe this tool helps me build relationships with prospects, that improves their confidence in my resources for evaluating their situation and to give them strategic insights.
Their SEO content template tool is also a great one for beginners. You have to just put the keyword you want to rank for and the target geo and it will provide you a template to do that. It'll tell you the keywords you need to use in your content and on-page elements and the domains from which you need to rope some backlinks to make your piece rank on the first page.