AC and DC (for grid power) each have advantages and disadvantages. The main ones are:
Its easier to generate AC than it is to generate DC. AC comes directly off the coils of a generator. You need rectifiers or switches (brushes) to convert it to DC. Also, if you use only the voltage from one coil and convert it to DC, it will still be pulsing DC. So you need to use a lot of coils where the pulses from the coils come at different times. That way if you combine the pulses from all the coils you end up with an almost smooth DC signal. But it still isn't perfectly smooth. You can smooth it further with capacitors, but high power applications would need massive and extremely expensive capacitors.
When (non-pulsing) DC is sent through power lines, far less electromagnetic energy is radiated from the lines, which means less energy is wasted.
Both AC and DC suffer from energy wasted because of the electrical resistance of the lines.
Electrical power is proportional to the product of the current (electron flow) and voltage (electron pressure). If you use high voltage and low current, the resistive losses in a long transmission line are less. So Ideally you convert the electricity to high voltage and low current before you send it a long distance through wires, then convert it back to a more reasonable (safe and easy to manage) voltage at the load end. Conversion of AC is done with transformers. Converting DC in this way is profoundly more problematic.
The simple voltage/current conversion is also very useful within appliances.
Many appliances need DC. So the AC must be converted to DC. However, they typically need a certain DC voltage. Since conversion of DC voltage is more complicated (and costly when large power is involved) this is still a pro-AC argument, because converting AC of one voltage to AC of another voltage is easy (with a transformer) and converting low power AC to DC (for a household appliance, for example) is easy with a rectifier and small cheap capacitor.
