Game Engines (Help Choosing)

[nemesis567]

I've been searching around for game engines and I've come along severall dozens of them. In the end I got a list like this:

-Ogre3D;
-DX Studio;
-UDK;
-Blender Game Engine;
-CryEngine;
-Horde3D;
-JME 3.0;
-Delta3D;
-Unity;
-HPL1;
-Irrlicht;
-C4;

After this, I narrowed my search to full featured open source engines and I obtained:

-HPL1;
-Horde3D;
-Ogre3D;
-Irrlitch
-Blender Game Engine;
-DX Studio; // I didn't exclude this because I have a pro comercial license(for free), and it might be of use depending on the flexibility of itself.

Now, I've got these 5 options left. Both Horde and Ogre are only graphical engines so I'd have the trouble to create my own development tools, but I quite like Ogre. Horde3D seems more immature, but is also a quality option.
I don't exactly know Blender Game Engine, but I know it's lacking lots of features and it's very immature. Irrlitch is not the best nor the worse.
DX Studio has got a nice interface, it's full featured and is a full-fledged game engine.

My objective is to learn the mechanics of game engineering and to build a small project(probably alone, so it's a simple project). All the engines mentioned are built under C++, so understanding them and modifying them wouldn't be much of a problem.

I'd like to know(since I've been trying to choose one for more than a week now), which one should I choose. Any engine I'ven't mentioned can also be recommended. Anyway, I really appreciate your help.