I don't know about Podia, but I have had exposure to Kajabi, Thinkific, and Teachable. I've also seen the challenges that come with doing it through WordPress plus plugins. Also, I worked for a year with a company whose sole purpose and focus was to help course creators to sell their work and be successful.
Here's my opinionated take:
Thinkific and Teachable are good beginner-level options, especially if you're not very tech savvy. Like others have said, they don't come with great marketing tools, so you'll have to solve those problems a different way. But if you're looking for an affordable way to host your online course behind a paywall without needing hardly any tech skills, they might be a great option for you.
Working with a WordPress + plugins platform can either be very difficult or very effective for you, depending on your tech skills. If your skills are good, or if you have the ability to hire someone, then go for it. If you don't, you're going to constantly be running into issues trying to integrate your systems (CRM,
email marketing, payment processing, calendar, call booking, ad traffic, landing pages, etc). Getting reliable stats on even simple questions like "How many signups did our ad drive last week?" can be a nightmare. If all that sounds easy to you, though, and tech integration is fun and not daunting, this option gives you the most customization and can be by far the most powerful. It allows you to use best-in-class options for each aspect of your marketing funnel. With any of the "all-in-one" options out there, you're limited to their tools. You have to trust their email deliverability, their calendar to work properly, their CRM to keep things organized the way you want, etc. Sometimes these things don't work (or stop working). If you're in WordPress and a certain app stops performing the way you want it to or you want to upgrade something, you just do it. If you're in Kajabi or Kartra or a similar platform, and one aspect of their software is problematic, you'd have to either put up with it or go through the hassle of switching platforms completely.
Kajabi - This platform combines course hosting with marketing tools like emails and landing pages. From my experience, the interface is fast, powerful, and impressive. It's easy to figure out and much quicker to get you up and running than if you go with a WordPress option. The student-facing interface is also clean and professional. If the price of Kajabi is not an obstacle, I'd say it is an easy choice. Stuff works well and you are able to focus more on creating your content than needing to run around solving tech puzzles.
The platform I have chosen to go with for my own use is New Zenler. It is built to be a Kajabi competitor, but it is still in Beta right now, so the pricing is a steal compared to Kajabi, and if you get on board during the beta pricing, you stay at that price for as long as you keep the software, no matter how they increase prices for new customers. I've been really impressed with the tools and the level of thought they have put into it. The only thing I've found that you can do on Kajabi that you can't do on New Zenler is host your own videos. You have to host them somewhere else (e.g. Vimeo) and embed them into New Zenler. I've found New Zenler very easy to set up and manage, and I haven't personally run into any "beta bugs." So if you like the idea of a platform like Kajabi, but the price is a bit steep for you, New Zenler might be a very attractive alternative. To join, you need an invite, so if anyone would like one, just message me and ask. With an invite, you can get access to all the tools for free to see what's included.
Hope this is helpful!