When comparing Li3 vs Phalcon, the Slant community recommends Phalcon for most people. In the question“What are the best PHP frameworks?” Phalcon is ranked 6th while Li3 is ranked 10th. The most important reason people chose Phalcon is:
Since the framework is and extension built in C it's extremely fast and efficient. It's actually one of the fastest PHP frameworks, and according to some benchmarks it's the fastest framework out there.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Unified relational and non-relational database API
Lithium has unified the relational and non-relational database APIs into a single one. Being one of the few frameworks to do it.
Pro Robust plugin architecture
Lithium makes use of PHP namespaces to create a powerful plugin architecture. Almost every component of the framework is replaceable.
Pro Fast Bootstrap & Autoloader
This framework loads faster than most due to its class autoloader. It is flexible as well and handles older classes - but requires the developer to define transforms here for naming convention, includes, etc. Many other frameworks use Composer for autoloading and that significantly slows down their bootstrap time because Composer's autoloader is extremely compatible without much developer interaction (it does not require as much involvement for autoloading legacy libraries). So it's a trade-off, speed vs. a little bit of up-front work.
Pro Integrated unit testing
Lithium comes with integrated unit testing. It also has a test dashboard.
Pro Aspect inspired filter system
Lithium's filter system is based on the paradigm of Aspect-oriented programming which aims to increase modularity by separating cross-cutting concerns and helping speed up development.
Pro Great for building an API
Lithium can return JSON and many other formats from the same actions that render templates increasing productivity in many cases. It handles a "type" key in the route which allows it to render various responses with different Content-Types. This is incredibly useful and easy to extend. This combined with closures in routes makes Lithium a very good framework for building a RESTful API.
Pro Extremely fast
Since the framework is and extension built in C it's extremely fast and efficient. It's actually one of the fastest PHP frameworks, and according to some benchmarks it's the fastest framework out there.
Pro Open source
Phalcon is open source and is available under the BSD License.
Pro Uses Volt template engine
The Volt template engine, which is embedded into Phalcon itself takes it's inspiration from the Jinja template engine and as such it's nice to look at, with a clear and understandable syntax.
Volt also compiles very fast, like Phalcon itself, so it avoids being a bottleneck for the framework's overall speed.
Pro Very flexible project structure
You can set up the base project as you want. It's very flexible
Pro Clean and light project code
Since the framework code is not in the project directory, the code is light and clean.
Pro Customizable with Zephir
Zephir is a high-level language designed to create PHP extensions easily by PHP programmers with no knowledge in C.
Zephir does this by compiling directly to C and then the C program is in turn compiled to be run as a PHP extension. This, coupled with the fact that Zephir's syntax is very similar to PHP makes it a perfect way for PHP developers to use it for customizing Phalcon.
Pro Loosely coupled components
Some components can be used as standalone packages like models, views, etc..
Cons
Con Less than ideal documentation
Documentation is scattered so it takes a little while to learn and figure some things out.
Con Not for shared hosting
Phalcon needs root access to install the PHP extension which is written in C. Developers who plan on using Phalcon must use VPS or Cloud Hosting with root access available.
Con Require good programming skills
Not so easy to use if you want to gain the best from it.
Con Debugging requires knowledge of C
You need to be a C programmer to debug Zephir or C code. Or if Phalcon is not maintained anymore and you have a problem and don't have much skills in C, you will be hard-pressed to find a C programmer to fix it.