T3D is a great game engine, and one of the best, the problem is the documentation, now the API documentation is complete, but it's more difficult to find some good videotutorials, or good posted tutorials, another thing are the collisions, I have several problems with it this days, I posted it in the forum but anybody answer me... The price it's very cheap and you get with it the source code. It's multiplatform, the normal version support: PC, Mac, Web browser
Unity, now it's one of the best game engines (really no, but the company has a lot of marketing, and it's really easy to use). You can found in it the deferred lighting, deferred rendering, interesting tools... the price it's high, 1500$, the free version it's very limited. It's multiplatform, the normal version support: PC, Mac, Web browser. Now you can get the other versions for free at the 8 or 18 April (android and iPhone, but just the basic version and not the pro).
UDK, it's maybe the best option if you want to make games por PC or iPhone, it's Unreal Engine 3 without the source code like in the full version, a lot of tools for development, integrated geometry editor, a lot of post-processing, shaders, a great optimization for all and it's really simple to use. The price it's 99$ or 2500$, it's depend, you can read the license in the web of UDK.
Leadwerks, easy to use, cheap and powerful game engine, it only does work on Windows. You can use Lua, C++ or both in your game. This community will answer almost always, you can found good people here. Leadwerks have a problem with the physics, and for it, you can't scale the objects (it's correct?). The API it's really really simple to use, it's like Blitz3D (more or less), you need a good hardware for use Leadwerks with good frame rate.
That's my opinion!