I’ve found google trends to be an interesting way to see if a keyword (and by extension a niche) is growing or shrinking, and whether it’s seasonal or not. I can’t think of any other tool out there that can reliably tell you this information, so that’s really useful. Also, if you’re building a site, especially an authority site, getting onto something that’s trending upwards is a fantastic idea.
1) SEMrush - I believe that among all the 3rd party software, SEMrush has the largest keyword database. Their search volume data is pretty accurate and aligns with the Google keyword planner. Also, based on the type of content that needs to be produced (i.e. informational, transactional, etc.), one can utilize different filtering options available in it.  

If you get an "Action Against Links" notice - there is no plea you can send. Your site or some pages of it - would basically have a lot of rankings. To fix things you need to fix links and any other on-page and other issues and wait for the re-crawl to happen. Since the Penguin algorithm is not real-time... you will see ranking gains faster and you do not have to wait for a data-refresh to happen to see any benefits of your link purge or SEO fixes.

Moz Keyword Explorer - Input a keyword in Keyword Explorer and get information like monthly search volume and SERP features (like local packs or featured snippets) that are ranking for that term. The tool extracts accurate search volume data by using live clickstream data. To learn more about how we're producing our keyword data, check out Announcing Keyword Explorer.
Jaaxy keyword research tool is a web-based tool which requires a membership to use. Providing High-quality SEO keyword research information to the user to allow them to produce content on their site that will rank and get actionable traffic. Jaaxy pulls information from Google, Bing, and Yahoo, to show the most relevant information regarding keywords. Not just pay per click data, but the right data that shows you what you need in order to properly put together a post or a page and get it on page 1
Keyword research can also lead to great ideas for your business, services and overall marketing strategy. Keywords can be a window into understanding what your customers need. In this regard, your content strategy is about more than gaming the search engines. Keyword research is about connecting with your audience. If you ground your research in knowing your customers, the results can aid you in providing better products and services and increasing your brand loyalty.
SEO Power –This takes into account the three other metrics above and determines if your keyword is a good candidate to get ranked, the indicated number is a % chance of ranking on page 1 for your keyword provided you have good content. If you can get ranked, you WILL make money online as long as you provide quality content when people find your article.

The experts love SEMrush, but will you? Take the tool for a test drive and decide for yourself. For a limited time I'm giving all my readers an exclusive one month free access to SEMrush PRO. You'll get unrestricted access to all the tool's features. If you decide SEMrush is not for you, cancel anytime during the one month trial and you won't be charged a penny. 
I have use Jaaxy for my website and I think it is a fantastic program highly recommended. I use I ask a key word research tool for my website but I was not aware of the other areas that it could be used for that you have listed in this article. With the new latest updated feature and the fact you can try it for free what do you have to lose. Thanks for the great article.

Yes Jaaxy has it all really. Not just Keywords and an Awesome new Rank Checker but also competition information and other methods for searching. Much More under the hood than what is a first glance..Highly recommend getting in with Pro Or Enterprise BEFORE SEPTEMBER so you can keep the current price structure. Those in after September will be subject to new prices..I am Glad you like jaaxy, keep using it and you will see how accurate the data really is.
It’s important to note that entire websites don’t rank for keywords — pages do. With big brands, we often see the homepage ranking for many keywords, but for most websites this isn’t usually the case. Many websites receive more organic traffic to pages other than the homepage, which is why it’s so important to diversify your website’s pages by optimizing each for uniquely valuable keywords.
You can find broken internal links from within the Search Console. You need to attend to each warning appropriately telling Google that you have fixed it. Having excessive 404s will hurt your site if they are really 404s, because anyone could escalate the 404s by pointing randomly to pages that don't exist from external places, which is why this is not that big of a deal - but should be looked at.
First of all Thank you !! for sharing our post on social media, that really helps get the word out to folks who may need to know about how awesome Jaaxy is. As far as the comparison, well they are both good tools, I will say that the Keyword tool inside WA portal in accurate and has very good useful information, I use it as well. It is however not a complete suite of tools like Jaaxy is, with the Rank Checker for 3 Major search engines, and the search analysis features and the “alphabet soup” search which is amazing as far as relevancy for any niche.. I have found Jaaxy to be extremely accurate in the data provided and as you can see, my ranks are showing as much and this website is still fairly young.  I have now sent 4 consecutive posts to page 1 or 2 within minutes after posting, simply by using the data Jaaxy provides and following what we have been taught on how to use the data.
The WA Keyword tool works well also and I am glad you like it. I use it as well. The reason I prefer Jaaxy is because it is an entire suite of tools in one package for an affordable price. Good choice to wait until you can budget for it. The free version gives a good taste of what is available but the paid versions both Pro and Enterprise are truly game changers. Once you make the leap you wont go back.
I use Ahrefs to find ideas for keywords to add into content, and content to create around keyword opportunities. I like how Ahrefs shows keyword difficulty, search volume, traffic potential (how much organic search traffic it’s possible to get when you rank #1 for a parent topic keyword) and lets you group keywords together to create lists. It’s really useful.
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.