Recs.
Updated
SpecsUpdate
Pros
Pro Major usage
It's used as a primary option for backend web dev, has a large community and is very versatile. According to the 2015 Stack Overflow Developer Survey (26,086 people surveyed), PHP was the 5th most popular/used language at 29.7%.
Pro Easy to find devs
You can find a dev team, dev companies or freelancers to create/maintain the project very easily.
Cons
Con Mountains of poor example code
PHP's place as the early go-to language for web development has littered the web with example code that's outdated at best. Unless you're already familiar with the language, it can be hard to know if code you're looking at is outdated or otherwise leading you in the wrong direction.
Con Most tutorials are out of date
A lot of very bad tutorials are still widely circulated among beginners, and these tutorials teach very poor programming practices.
Con Poorly designed language
Despite its widespread use, PHP is generally looked upon poorly from a design point of view. The consistency of function names and function argument order, lazily and borderline non-functional implementation of object oriented programming, slow version adoption (the PHP you learn right now may not work on every webserver you'll work on), and a focus on "hacking things together" rather than "doing it right". These are all very common complaints when it comes to working with PHP.
This scenario is changed after the release of PHP 7.0 with more object oriented approach, high performance and scalability.
Con Developer community has a reputation for being of low skill
The low barrier-to-entry for PHP development encourages low-skill workers to use it. Using PHP means joining a developer community with a poor reputation and may affect credibility of finished product.
Con Immense catalog of insecure frameworks
The most serious security problems in websites on the web today are almost universally found in popular PHP frameworks, CMS platforms, libraries and code samples, almost all stemming from poor language design, bad tutorials and awful resources.
Recommendations
Comments
Flagged Pros + Cons
Pro One of the most common languages
According to the 2015 Stack Overflow Developer Survey (26,086 people surveyed), PHP was the 5th most popular/used language at 29.7%.
Out of Date Pros + Cons
Con Poor performance benchmarks
PHP performs poorly at many common tasks. Benchmarks are available at https://www.techempower.com/benchmarks
Con Bad performance
This only applies to PHP < 7. For example, PHP 7 is 3 times faster than Python 3.