GTmetrix

The first thing I liked about this tool, is it's super simple to use as well as it's effective. GT-Metrix added a new feature called Speed Visualization which can help me to track every second loading report and the obstacle that blocks the speed index. This tool especially provides two types of score, performance and structure which is very helpful. They don't even just show the website loading speed result. There is a TOP ISSUES tab with a complete guideline for troubleshooting methods. As a developer, I take help from this tool a lot, it's really superb!

GT-Metrix can't show the exact loading speed or performance in the report. If you scan the site URL for the first time, you'll not get the same result if you scan it for the second time, this is a weird thing. I provide speed optimization services to my clients. After finishing the speed up process, clients check the site performance on GT-Metrix. But the performance they got from their side, not match what I'm getting on my side, so this is another annoying thing about this tool. Scan location of GT-Metrix always shows from Vancouver, Canada, but I'm not in this location. It doesn't matter from where you are scanning or using the tool, it will show Vancouver, Canada location. I think this tool needs to improve these things.

I manage many websites for my customers and I do like the idea of automatizing most of the checking I have to do and be able to access the data whenever I need to without having to set many things up every single time.
Plus it is that userfriendly, most of my customers can get the info on their own and ensure everything is fine on their website without being forced to ask me to check things up.
Finally, the reports are complete enough to find solutions about anything that would turned to be wrong about your content, so when new algorithms emerge, you won't only know your contents don't pass the system but how to correct things so they will.

I sincerely have no idea, that's exactly why I never looked for another software.

Last year GTmetrix updated their protocol so it's now fully up-to-date with the latest Google metrics. Just by having an account, you have a choice between various different locations to test your website load speed from.

GTmetrix gives a lot of different views, metrics and important tips that help you optimise your websites.

Not many tools have the possibility to enable video view so you can see exactly how your website is rendered in a certain browser and what the actual loading time is. This is very handy.

It might be just my websites, but I'm often getting very different results between tests, which can be very frustrating. There's always this doubt whether a website is trully fully optimised when you get A ratings, B ratings and then suddenly an E rating. But again, that's probably not their fault.

The limits on the free plan can be pretty frustrating. But they're a business so they obviously need to have limitations on their free plan in order to have more people upgrade and make money.

I have had very good experience with GTMetrix, and believe me I have used many in order to not only measure the speed of my site, but to correct many aspects that prevent an effective SEO positioning.

For me, one of the best tools to measure the speed of loading the website, in addition to this great advantage, also lists the errors you might have within a site and the recommendations to improve or minimize such errors.

This tool has given me a lot of value when auditing one of the websites, since it lists the values ​​of each of the parameters that the site has and tells me how long each part of the code of the page takes. So with these values ​​I can optimize my website.

The truth of all the tools, this seems to me the most complete, because what they lack to others this one has it and it is to be able to compare several websites.
The only thing that would add would be other servers, since it only has a location like Canada.