I use many scripts, the mentioned on posts and others, only i have not the oportunit to test SMF, that because i find MyBB and it's very best option for me.
Why, because i like free scripts and codes, i can manage and test without any problem xD.
In my personal opinion, every script have their own vulnerabilities and they have some particular things. I like vBulletin, but is a paid software, and only can manage sites of friends who pay the licence every year, but it's good.
On security i have to tell the script more hacked is phpBB, many sites of vBulletin and MyBB, SMF, are hacked too, and official sites too xD.
But honestly i have my own preferences on every script i test, and for many reasons i think MyBB is one of the best options for programmers and newbie users to start a forum site xD.
If you talk about themes or plugins or some mods, you can see on my site i have my own theme, my own plugins and i use another plugins to make more pretty cool xD. My site is a very powerfull site, not secure at all or invulnerable, is only a site and i feel fine with this xD. I'm still using MyBB since 2 years ago and many other scripts and my favorite one is MyBB for my own reasons, i like vBulletin, but i don't want to pay if i wont use like many other users or sites xD.
You can use every script and finally you have your own experience, if you like someone you have to test it and i have that opinion, you have to test every script to choose one xD.