Which is the best platform to create a free blog on?
As I've been using both platforms simultaneously, I've come across the conclusion that WordPress can be your best fit if you intend to buy a domain name and get a premium plan for hosting. Wordpress is a beast and it has a lot more that we still need to explore. It has plugins which are simply missing in the Blogger's case. Blogger doesn't support any plugins but it does support Themes, well it's the same case with Wordpress and the themes for wordpress are highly customizable.

Now I won't say that Blogger is not good. Blogger is best for beginners who just want to build an online presence and get viewers to know you. Blogger is best, and I've been using blogger as my main blogging platform for a year.  And trust me I've got monetization and it's really nice that google is still helping blogspots to get SEO.  I believe that Blogger can be an Ice breaker for many like me, who don't have money to spend on hosting and domain as a beginner.

HISTORY OF BOTH PLATFORMS :
WORDPRESS:
Initial releaseMay 27, 2003; 18 years ago
Back then it was still one of the best platforms to get started with. And the best thing is It's still one of the most used web builder to start with.

BLOGGER:
LaunchedAugust 23, 1999; 22 years ago
The oldest one but has many things to get work going, And the best thing about blogger is that it's free! There are very limited inbuilt themes but there are many third party themes on the web you can use to customise blogger.

Currently Active Users :
WORDPRESS:
As of 2021, there are about 1.3 billion total websites on the web. More than 455 million sites use WordPress.

BLOGGER:
Blogger (Blogspot) powers 617,000 blogs.

CONCLUSION:

Both platforms are great and have their own pros and cons, I won't judge which one is greater than the other, But my personal favourite is  Blogger as I currently use it, I don't need fancy plugins for mails or contact forms or anything, Blogger has everything I need in it. I just love using blogger for it's simplicity yet customizable layouts.