Some historic part one that (the old Edison vs. Westingouse fight):
Every voltage drops when transported over the line. If you go down a few kilometers you start with 600v and end up with 300v or less on the other end. You would need an DC-DC voltage regulator for every house, which is expensive (well, nowadays not that much, but back then very very very...).
Now we kick in AC. We still have the voltage drop, but we can use cheap-ass transformers which require no special parts and can work for decades, even centuries, without needing any maintenance.
See the history about that, there is enough around on the net ;).
The reason for DC are very long cables (1000 km or more). The speed at which electricity (here: signal speed, not electron movement speed) is transported in copper is above 200000 km/s.
So if you use AC on a long line the signal gets an offset between both ends, enough to produce quite an amount of loss and problems. This is where high voltage DC is used. China is currently building the most long land lines that way, but we have quite an amount of those in Europe as well.