When comparing UDK vs Leadwerks, the Slant community recommends UDK for most people. In the question“What are the best 3D game engines?” UDK is ranked 17th while Leadwerks is ranked 31st. The most important reason people chose UDK is:
UDK has an extremely large toolset that allows creating almost anything without having to use a 3rd party tool or plugin.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Large toolset
UDK has an extremely large toolset that allows creating almost anything without having to use a 3rd party tool or plugin.
Pro Triple A track record
UDK is an engine used by many big name companies for popular games such as the Gears of War series.
Pro Very good entity system, did have GUI functions, easy to use terrain editor with vegetation system.
Good API tutoials, workshop elements which can be loaded from steam.

Pro Both Windows and Linux supported
Pro Built-in level editor
Has an acceptable 3D map editor that is easy to use.
Pro Versatile flow diagram script model
Leadwerks's flowgraphs resemble flowcharts where each box represents a function or value, with connections between them representing program flow. This provides a better at-a-glance indication of game logic than a simple list of events, and makes complex behaviors easier to accomplish.
Pro Community forum offers plenty of support
It makes game developing much easier if you have someone backing you up when you run into a bug or other issues, and get replies within hours .
Pro Decently sized library of tutorials for both Lua and C++

Pro Very clean and easy C++ API

Pro Lua scripting support
Pro Reasonably priced
Standard edition of Leadwerks costs 92,99€. Additionally, it often goes on sale on Steam.
Pro C++ scripting support
Pro Terrain editor
The terrain editor allows sculpting, paint, vegetation placement and importing of external maps. Especially the painting is done very well and can lead quickly to very professional looking results.
Pro Easy to use API and scripting language
Cons
Con Superseded by Unreal Engine 4
Con DevKit only runs on Windows
Even though UDK can deploy games to run on multiple platforms, including Mac, it does not feature support for development on Mac.
Con Limits games to FPS
UDK was originally developed for the FPS, "Unreal Tournament", and it certainly shows. While UDK is a very powerful engine, it takes quite a bit of work to make it do something other than an FPS.
Con Little to no support
This product relies on community support, although some members are helpful and quite approachable they don't like to share their secrets with people that are new to programming.
The product is sold as a Full featured platform but it seems to more in the Alpha stage of development as a lot of the good aspects where taken out in previous versions.
Con Has a track record of broken promises
Con Forums are poorly run and censored
Con Highly misleading advertising
Con Only prefabs made with the Leadwerks IDE could be used.
The two main problems for me is that C++ is not as easy to use like LUA. The IDE should also support C++. The secons is that only prefabs can be used which are made with the IDE. So you can not easy made a game that can be modded by the user.
Con Weak out-of-the-box AI
The only AI movement function is going in a straight line.
Con Very buggy
Leadworks is a not complete, it's a work in progress. As such many parts of the engine are clunky, especially the level editor.
