Not one checker on this list is perfect. The only way you'll get a perfect editor is to learn the rules of grammar, spelling and comma usage yourself.
All these editors miss something. I've taken a purposely misspelled piece with grammar and comma issues to test them. Every one of them missed a crucial problem. You'll have to decide your problem areas and use the editor that will help you the most.
This basic grammar checker will find words that have other spellings and highlight them for you. For example, it will highlight the word "hole" and suggest "whole" instead. It doesn't find missing commas. Pretty basic.
I like this editor. It's the one that catches most of my poor word choices. It will highlight cliche phrases and word repetition. What I love most about it is the sticky sentences report. Glue words are unnecessary words that clutter a sentence and make it awkward. Pro Writing Aid will show you those sentences. It won't fix them for you, but it will identify them. It does not catch missing commas. **Personal Favorite**
When I first started writing professionally, I used Grammarly. It was the most thorough editor I'd found. It found so many problems with my writing. I spent $30 a month for their subscription service. If you're serious about writing and need major help, I'd suggest them. After a year, I was able to understand the mistakes I made. Split infinitives, missing commas and fanboys. It's been a long time since high school. I stopped using the service, and didn't see a loss in the quality of my writing. **Worth the Cost for Professional Writing**
This editor finds the same errors as a Word program. I know some people who love this, but it's never done much for me. It's available on Wordpress.com, which is the only reason I mentioned it. That might be a plus for some of you bloggers who use Wordpress.
This is another that I like for certain writing. It checks for plagiarism and will give you a letter grade for your work based on readability and word choices. I haven't used it in a while, but I notice it now has captcha, which I find to be a pain in the butt. It's still a worthwhile, free editor to use if you don't mind squinting at the numbers! **Great for School Projects**