It is too broad to answer. Underground coal mining is based on the rock mechanics, So FLAC, ANAYS, Abaquas are widely used in coal mining. For underground coal mining in U.S., the NOISH recommends the following softwares and you can download from this website: http://www.cdc.gov/niosh/mining/works/productlist.html.

There is no best software. It depends on your question and what kind of problem you will solve.

I also recommend FLAC3D

I personally used it to model subsidence of shallow tunnelling in urban environment and a friend of mine used it for coal longwall mining and its subsidence modelling

Xu, thanks for valuable advice

You can consider using UDEC.

I agree with Xu Tang. First you have to give information what phenomenon you want to model?  

It depend on your model characteristics: rock or soil, joints, and .... But for simple simulation in soil medium, I suggest Plaxis2D software.