3D Studio Max

3DSmax is the best choice for GoldSrc modelling as Half-Life was made with it and has .max files and BIPED rigs in the Half-Life SDK. Note that the SDK .max files have to be resaved after opening due to the file format age. If you cannot open them for any reason or get errors/crashes, try using "merge" to merge the old file into a new scene. 3dsmax generic units are identical to Hammer units for scale.

My tutorial will cover three different exporters which you can use depending on your version of max or preference of options.

Wall Worm Model Tools

Game Zombie