There are many free blogging platforms out there. Blogger and WordPress are two of the most popular free options. Blogger is owned by Google so it has some advantages like reliability and security, which is important if you’re running a free blog, as some of them won’t have that top-notch level.
In my experience, most of the drag and drop free blogs are a pain to work with. Two options that are pretty easy to use are Wix and Tumblr. I’ve personally had some pleasant experiences with both of these platforms.
Check out some of these links before making a decision:
http://www.wpbeginner.com/beginners-guide/self-hosted-wordpress-org-vs-free-wordpress-com-infograph/ – This will explain the advantages and disadvantages of the wordpress.com vs .org.
http://howtomakemyblog.com/blogger-vs-wordpress/ – This is blogger vs. wordpress.org. Finding a comparison of the two free versions was difficult to find.
Conclusion: Blogger might be the best bet for an online journal/diary. It’s slightly easier to use. Aside from that, WordPress is likely going to be the route you want to take. Check out the various tutorials and that might help with your decision.
If you’re ready to get started, here’s some info and tutorials that should be very helpful.