I went through the same process as you too before deciding to use django. I am a Java programmer during the day and I want to have a pet project that I can make during my spare time. So I got myself a VPS with the cheapest plan available. I installed Java webserver and deploy a Grails app, but it turns out that it needs a bigger memory. Then I realized that Java webapp needs a large memory to get running. So I went to look for a non-Java framework. I didn't have much criteria at that time other than it can run smooth on my current VPS plan.
I took a look at django and I was amazed that:
- It is so simple and easy to get started. It only creates small numbers of file (compared to Grails)
- It has many built-in feature that Grails doesn't have:
- RSS feed framework
- Commenting system
- The admin system (you gonna love it, it's like scaffolding only better)
- And many other webby features that takes time to create
- It needs less memory to get started, but it can also scale really well
Other than that you're just going to compare Groovy and Python. If you're a Java programmer you're going to love Groovy syntax as it is really close to Java. But python is a good language too (despite that many people don't like it's syntax).
If you want to use JavaFX as the front-end, then you can use django just to return JSON data or XML data, and you can do this easily because it has a built-in serializer to do this.
So all in all the criteria drills down to what you need and what you already know.