Hey Alex – this is a good question. No tool is going to be spot on. My advice is to not look too much into the accuracy of the metrics, but look at it more as a relative measure. I’m finding Ahrefs to be a good barometer for keyword competitiveness, but I’ve also heard great things about KW Finder lately. I think it’ll more come to personal preference. Both are solid options.
Of all the tools listed in this article, Moz Link explorer is an old one & quite popular.  If you want to compare backlinks between two or more domains, Open Site Explorer is worth trying. This tool works best when you have a paid account of SEOMOZ though a free version of this tool is good enough to get you started checking the backlinks of your site and the sites of your competitors.
To use this feature, click on the second tab that you will find on the top right bar. Type in the keywords that you want to view the performance of, and also type in the name of your domain. Hit the search button and allow the software to find whatever you are looking for. Site rank will analyze the top page of Yahoo, Google, and Bing to find where your site could be. Jaaxy will also show you how your post or page is performing, so you will know if it is climbing or dropping in the search.
3. Ninja Outreach: Full disclosure this is my own tool, and it is actually an outreach tool, so you may be wondering how it plays into Keyword Research. The fact is there are quite a few data points that NinjaOutreach gets for me that I find useful in keyword research, such as the articles that are ranking for the keyword in Google, their domain authority, their page authority, the number of backlinks they have, and other social and contact data. It's pretty valuable stuff, especially if there is going to be an outreach campaign tied into the keyword research. I wrote a great article with Jake from LTP showing the combination of the two tools.
You can also block certain files or folders with passwords to the public or from certain bots. For example if you are still setting up a site and don't want it accessed - you can block it. This is very useful when building your Private Blog Network, because you can block tools like Ahrefs and Majestic from crawling your PBN site and hence hide any backlinks to your main money site from being discovered by your competitors (and therefore hide your PBN entirely). You can read up on Private Blog Networks and how to build them in my PBN guide.

1) Google Keyword Planner: This tools is fantastic because it can help me to identify long tail keywords for my niche. It is official Google’s tool and it has the recent trends and keyword variations. For example you may think that this keyword is great “buy ipad air in liverpool” but Google may suggest “iPad air sale Liverpool”. Yes, not often it is accurate but when I’m using it alongside the other tools – I can get clear idea.
As for duplicate content, Google gets confused when you create and publish articles with similar content, and this eventually leads to indexation issues. Keyword cannibalization happens when the owner focuses his effort on ranking for a particular keyword from several different pages. When this happens, Google won’t acknowledge multiple pages; they’ll only focus on the best one thus making the other ones useless and inaccessible to search engines.
There is a myriad of search algorithm updates, erratic market trends, increase in competition, among other things, all the more reason for you to be always on the move. With the help of the different tools that you can easily access with just a google searc>h away, all of these can be done in a snap. If you are committed to these practices, SEO ranking would just be a light feather on your workload.
However, this does not mean you cannot topple them. It just takes more of an effort in terms of content as your page has to build the trust. That is why you will see the "Google dance" happening for fresh content from a site that is not yet trusted or is not very authoritative. Google gives your page a chance and measures user click-throughs when it pushes you to certain spots in the SERPs and then measures user engagement levels when the traffic hit your site through those positions in the SERPs.