@sda I have run mastodon, it was bulky and slow compared to GNUSocial. My instance has been up a couple months, but I used to run gnusocial.me as well. Technical differences:

#GNUSocial has (And Mastodon does not):
- PHP
- Plugins, modules, etc (easier to customize)
- Runs in Apache, Nginx, lighttpd, etc
- MySQL support
- Windows Support with IIS and PHP5
- User polls (Voting system)
- Groups
- JSON, ATOM, and RSS feeds for accounts and API
- True support for SSL/TLS
- Admin can set text limit. (p2px.me can send out 2000 char. notices (Or toots as they are called on Mastodon))

#Mastodon has (And GNUSocial does not):
- Content Warning System (Allowing users to hide posts)
- Privacy Settings (GNUSocial kinda has this, but is way too limited)
- Runs on Ruby with or without docker (GNUSocial has docker support as well, but that is old)
- PostgreSQL with Redis Queue (GNUSocial can use redis queue as well like my instance does, but Mastodon uses it by default)
- Native Statistics page (GNUSocial needs a module installed for this)

I can't think of anything else at the moment. I prefer GNUSocail because it is written in PHP (Which I know and love, unlike ruby)

Let me know if you have any more questions, also fediwiki.info (Ran by me as well) has a great tutorial for installing and maintaining Mastodon AND GNUSocial. Check it out sometime.