Powder coating is very durable, also good for rust pitted frames as is quite thick and fills all but the worst of the pits. Be aware though that unless you have a full set of frame taps it is essential to mask up all threads as powder coat is as hard as nails. Also never get a silver soldered frame powder coated as you will get a loose set of tubes and lugs back
Spray painting gives one a greater choice of palette and finishes, but is generally far more expensive. Some peeps get precious about which method to use on vintage bikes but I'd only worry about that with something really special.
Just to keep this post legal, best I mention I'm drinking tea and eating choccie biccies at time of posting