debian

a) It just keeps on working.

b) They are conservative with new technology. This means that by the time things hit debian theyre well thought through.

c) The community behind debian is principled.

d) The debian package repository is very exhaustive.

e) They offer a small net install iso which is ~180 megabytes. This makes a fantastic foundation for a minimalistic linux install with a tiling manager (without pulling in monstrosities like libre office).