There is a lot of talk among Wix designers about the old blog versus the new. Some designers think there are more visual design options for the new version, but there are drastic downsides. Personally, I install the old blog on all my clients' sites because the features offered are still the best. If you are designing your own Wix website, I'd recommend going with the old blog app for three main reasons, which I'll enumerate here.
If you've used a fairly new template with a blog page already installed, chances are the pre-installed page is the new blog. If you are adding a blog, be sure to grab the green icon version from the App Market and not the gold one. See photo above to locate the difference.
Even if you have a pre-installed new version, you can delete it, then add the old version from the App Market quite easily. I'm not certain whether any blog posts you have already installed in the new version will transfer over to the old version, though, so be sure to have another copy of those posts before deleting the new blog app.
Don't use the so called Easy Blog, either, as it's a third party product that is disappointing. If you already have a Blogger or Tumblr blog and want to display that on your Wix website, you should be able to do so with one of the feed apps, but you won't get full management capability without still entering your Blogger or Tumblr accounts. That means those feeds will look stylistically different from the rest of your website.
Old Blog Advantage #1 - Scheduling Posts
With the old blog you can schedule when you want to publish a written blog post. That means that prolific weekend writers can set up several posts and schedule them to publish over a month's time, and not worry about this marketing chore for another 30 days.
You can also change an already published post to a different past date, in order to change where it is located in the blog sequence. Doing that, tho, could screw up some of the already earned SEO for that re-dated blog, so do be thoughtful about using that option.
Advantage #2 - Actual SEO Meta Tag Options
In the right side column of the editing screen for blog posts in the old blog, there is a button link at the bottom that is labeled Advanced. This is where you can adjust the URL permalink, the meta title, write up a snippet description that will show in Google, provide an excerpt from the post, and modify the title for better display on a cell phone.
Click on a photo you've added to the post to add alt text keywords or phrases to further enhance SEO.
Add categories and tags (keywords) to the post itself, then display a categories list or tag cloud somewhere on the blog page. The very outdated style for doing that is to use a right side column, but that display choice has been in disfavor for a long time among designers. The more current choice is to put the tag cloud at the bottom of the main and single blog pages, and a short categories list at the top of the main blog page.
Advantage #3 - Tools Available
In the old blog editor you can add multiple single photos, or a photo gallery (several pics grouped together). You can add video, audio, gifs, and html codes. An additional tool bar pops up when you want to change something in the text itself and have highlighted where you want the change.
As you can see, this additional tool bar looks quite familiar to standard Word tool icons. The red arrow shows text is highlighted, altho on your screen the highlighting will most likely appear blue instead of gray. These tools will make changes to the specific post you are working on at the moment.
Even more tools are available outside of the blog editor itself for universal changes to the blog such as centering the title of all posts, changing the styling of photos in all posts to use or delete a frame, putting more or less space between each post snippet on the main blog page, changing how the categories button appearing above the title appears, and so on.