Tungsten Dart Barrels
The surface of the barrel is covered by knurling or rings for a safe grip on the dart. Again there is a vast selection of different surface shapes, and combinations of them. And there is the possibility of a plain surface (which beginners are usually unhappy with). Again, it can't be said which variations are the best ones. Choose what suits you, what feels good and what you think you can handle.
There is only one thing you should avoid: painted surfaces. Paint might look good, but usually it makes the dart only more slippery. The probably only exception here is Unicorn's "gold" brand. These darts are covered with a golden coat (I don't know what material this coating is. But it's not gold) which they say improves the grip. I have not experienced any differences with these darts, but some people seem to like them. Try and find out for yourself.
An example of two world champions:
Dennis Priestley throws 14 gram darts.
Raymond van Barneveld throws 26 gram darts.
If you ask the average question now the answer will be 20 grams, but does this make sense when the weights vary that much?
For a beginner steel dart player I recommend a barrel weight between 22 and 25 grams, which is slightly on the heavy side. The reason is that you need to develop a basic throwing skill in order to reach a certain initial level of play with darts on the heavy side. You would probably reach such a level a bit faster with lighter darts, but lighter darts don't force you to develop a somehow decent technique which will make later improvement a lot harder. Heavier darts also forgive slight technical inconsistencies (in other words: errors) better than lighter darts -- I like to tell heavier darts more "good-natured" because of this. The lighter the dart the more sensible it reacts to what you are doing -- slight intentional adjustments as well as slight technical errors or deficits.
Once you have got some darting experience and a decent technique you may find the heavier dart not that convincing any longer because of its good-natured behavior. If you then think you could use a dart that reacts more sensible you should consider going lighter.
Soft tip players won't have that much of a choice for their dart's weight. The limit set by the machine operators and leagues usually is below 20 grams. If you are a beginner in soft tip the only advice I can give you concerning the weight of your darts is start at the maximum allowed weight.