Powdercoat is generally less expensive and more durable than paint. It's also generally less attractive. If you need a quick and dirty way to protect your frame fromt the elements powdercoat is the way to go, if you want to restore a beautiful old frame paint might be preferable, especially with pretty lug work as powder tends to go on a bit thick and mask some fine detail.

I'm sure there are exceptions. Certainly bad paint is way worse than mediocre powder. A really good powder coat job will look almost as good as paint and be more durable, but it will cost you.