Last days I've compared phpbb3, xenforo, invision, vbulletin and bbpress. In my opinion better to stay with phpbb.
Invision - expensive as hell, $200+$500 in modules to get phpbb features.
Xenforo is cheap, $140 but there is a problem with customization. Not so many styles, themeforest is almost empty and everything looks like xenforo basic style. Also support is very arrogant when you asking presell questions.
Vbulletin? It seems good but I remember competition forums about Android and there is one problem - massive spam. Here we have captcha no captcha system and if needed I can make android related question - there is no bot with android knowledge
BBpress - very interesting solution but lack of features, I would need to build whole forum script from hundreds of plugins. Many would be buggy so this solution is the worst.
I've decided to stay with phpbb - I know this script, before android journey I was modder and template maker. I will tune it for SEO and modify this template. As I said few times ago - this forum is place for years - not single action to grab your cash and forgot about you
I want to beat competition because I hate this guy