Characters in Gore are ranked from Light to Heavy. The balance between them is speed and size vs. damage resistance.

This means the lighter the unit the smaller and faster they will be, thus making them harder to hit. However they will also take more damage. The heavier the unit, the slower and larger they will be but will take less damage when attacked.

The best class to choose will depend on your own preferences and style of play, as well as the type of area you are in. For example lighter classes which are faster may fare better in large open areas levels, while heavier classes which can take more damage and are slower may be more dominate in levels which are mostly indoors and do not require as much distance to travel.

For you beginners, try playing the medium class first as a good middle ground to start, and try joining team games such as Team Deathmatch (TDM) and Capture the Flag (CTF) where you can respawn infinite times and most of all rely on help from teammates to stay alive so you can become used to the game and the characters.