All of the mentioned methods for acquiring bees have their advantages and disadvantages but for a beginner I recommend the following:
My first choice would be to start with a nuc because it's a complete conlony, only smaller in number; they have constructed comb and started storing food and teh queen has layed some eggs. The bees will be out foraging sooner since they don't have to start from scratch.
Bees in packages pretty much start from scratch without any comb, food, or brood so they'll require time to build comb before starting to forage for pollen and comb for the queen to lay her eggs. But if you know your source, and know you'll have to feed them, then packages would be an acceptable choice
Swarms, if caught by an experienced beekeeper, might be an acceptable alternative -- assuming the queen is in the colony. But I wouldn't recommend that a beginner go out and collect a swarm; unless they're with an experienced beekeeper to help.
Bees from another beekeeper would be OK if the bees are healthy and the hive is hygenic. You'd have to know what to look for to make sure you get a clean colony of bees. There are too many diseases that you MIGHT inherit. An exception here would be if the beekeeper is licensed by the state to sell bees. That means that the hives have been inspected by the state and certified as healthy and that the beekeeper is practicing appropriate management techniques.