There are two kinds of tips of a tungsten dart, which are steel tips and soft tips. Each kind of the tips both has their advantages and disadvantage. The details please see as followed:
Steel-tip: You have two options, fixed-point or moveable-point.
Fixed-point: This is where the point is solidly fixed into the dart, it does not move. This is the most common type of dart you will see.
Moveable-point: Guess what, these points move! There are a number of different varieties on the market, but the theme behind them all is the same, "Help decrease the chance for a bounce-out". When you throw the dart, you want the point to be fully extended. The hope is that if you hit a wire, the back-end (or barrel) will then move forward and force the point into the boards as opposed to letting the dart bounce off the wire and fall to the floor.
Recommendation: When I first started throwing back in the mid to late 80s, the boards were made differently. They had big round wires and lots of staples, especially those big ugly ones holding in the double-bull. Moveable-point darts were definitely the way to go. Now, things have changed a lot, board manufacturers have redesigned the boards themselves. Now you have staple-less boards (including staple-less bulls), diamond shaped wires, and even boards whose wires are completely embedded (can you say " The Bandit Board?"). If you are always throwing on real hard boards, or older type boards that don't have all the nice features, moveable points may be for you. If, like me, you're lucky enough to only throw on the higher quality dartboards, then they may not be worth the extra money. They do have one main advantage over fixed point darts and that's the ease of replacing the points when they are worn or damaged. Well, there's my two cents worth!
Soft-tip tungsten dart is a different story, you will need to check with your local leagues for the weight requirements. At the time of this posting, 16 grams darts seem to be a safe bet no matter where you are throwing.
You can get a heavier soft-tip dart, but some leagues and tournaments may ban them due to the construction or restraints of the machines that are being used. An opponent can challenge the weight of your dart if they feel it is too heavy.
Recommendation: If you're throwing soft-tip darts, go to the 14-16 gram varieties to play it safe. If you're just starting in steel-tip darts and do not have the ability to try out different weights to see what you like, I would start off with a 21-22 gram dart.