I started looking into GitLab and Phabricator around August/September 2014 for my company. My criteria was primarily based around something to assist with code review. Ultimately I went with Phabricator for several reasons:
1. Supports Mercurial - our repositories are currently in mercurial, and using any other tool would require switching to git (which we seriously considered while looking at tools).
2. Simple to maintain - if you have experience setting up other web applications based around LAMP, this is essentially very similar. The web interface even indicates setup issues to admins, from things which can cause issues to performance configurations in things such as MySQL and PHP.
3. The code review interface was more intuitive for myself and other engineers. From the command-line tool (Arcanist) to how it's conveyed to the user in the web interface. It did take a little time to fully comprehend and implement the process for using, but since implementing in Feb. of last year, after around 4 months we had near 100% adoption by the engineering department. The GitLab/GitHub interfaces I've found to not be organized intuitively -- the lifetime of an issue/changes seems (seemed?) more social-based and intermized where in Phabricator an Issue/Task is almost separate from the changes which can go into it, though they reference eachother easily.
>Also, do they pride themselves for writing this in PHP? I consider this an anti-feature, but this might be highly opinionated.
I had the same reaction at first (thought I wouldn't say it's pride?). In fact the first time I looked at Phabricator (~2012) I totally dismissed it for three reasons:
1. Written in PHP
2. Mentions pokemon on the front page
3. Marketed as "collection of open source web applications"
These led me to believe that it was at most some PHP glue some students hacked together to get different unrelated applications to play together. This conclusion is entirely wrong. I've since changed my mind about PHP - biased from earlier experiences there's no reason to think a reliable/stable application couldn't be built on it. Phabricator (I believe) started as an internal application at Facebook which has since become its own company. The code is very well organized (I've contributed some small changes), and there are some very bright people working on the project - I get the vibe that they genuinely want to solve the right problems rather than checking features off a list. There are very few dependencies on other libraries unless you specifically decide to enable extra features, and even then there's some support/documentation there to assist. Despite the light-hearted humor (see pokemon) that is a staple of the software (unless you enabled serious-business mode), the project is designed and developed by highly capable, quality professionals.
I couldn't have been happier going with Phabricator over GitLab.