It doesn't make a difference if you are just starting out in pool. Both are enjoyable and can be used to compete, but one offers more chances of winning. It is important to think about your own style and your game skill to decide which of the two you prefer.
8 ball can be a great choice for anyone who is just starting to play or someone looking for an enjoyable way to spend their free time. There are more chances to score and it is easier than 9 ball. The game is more difficult than any you have ever played. The rules of the game, including the rule to pocket the balls numerically, are important. You will also need to know how to shoot the balls.
With regard to the 8 ball you need to know how to make a play, when to put it in a pocket and when to let it go. If you want to make a run out, you will need to pocket all the balls on your side first, then make the 8 ball. Depending on the tournament, you might need to make a minimum number of pocket shots before your run out. But, you should be capable of hitting the 8 ball in only one or two shots.
There are many similarities between the 8 ball and the 9 ball. There are two options: you can use a triangle or slop to guide the balls to the right place, or you can use the 8 ball to guide them. A 9 ball cannot be pocketed. Only a handful of shots can be made on a 9-ball, and only one is the "Golden Break," meaning that you win regardless of previous balls.
You can take the Golden Break right after you have made your break. If you are able to make the shot, it is possible to win. However, you will need to have good feel for the cue ball, or you may be in for a rude awakening. You will struggle to make the 8 ball if you don't have it. While the rules for 8-ball will vary, in general you need to be exact with your shots. This game isn't as forgiving as you might think.
The major difference between the two is that 9 and 8 ball are a bit more difficult to master than 9 ball. However, it's more difficult to master. There are many national rules that govern 8 ball. You'll need to be familiar with them if you want to play. Also, 8 ball's rules may be slightly different to 9 ball.