[astrange]

Arithmetic coding is better than Huffman coding because it can use a fractional number of bits per code, while Huffman has to use a whole number of bits.

IIRC the only reason it wasn't always used for everything is patents. A secondary reason being that it can be slow if you design it without thinking about performance, eg if you use divisions.

[gliptic]

Huffman still has a performance edge for static distributions. ANS bridges some of the performance gap between arithmetic coding and huffman.

[astrange]

But there's no such thing as a static distribution :)