Oh, cool! An atom! Pick the coolest design and lightest design possible. That’s what really matters.
You see a cool design or color, I see potential for me to bend it half on the first accidental sprocket smash. Everyone is bound to bash their sprocket at some point so pick a sprocket that is thick and has minimal cut outs. If you grind often, try picking a sprocket with a built in guard.
Weight is not an issue when the component is 2x as thick and only 1 oz heavier.
The sprocket size is dependent on the driver size, the riders gearing preference and riding preference. A small gearing will make it easy to accelerate but lower the top speed. A larger gearing means the bike is more difficult to pedal initially but has a greater top speed. In return, the larger gearing will be best for fast fakies since the rider pedal backwards less since the cranks cover a greater distance. The smaller gearing would be best for riders who like to ET. The smaller gearing allows for ease of pedal in this particular trick.
The sprocket size can make a huge difference in bike feel. Since most BMX bicycles use a 9t driver we will use the standard driver size as a constant in the upcoming examples. To determine if you will need apply much pressure to the pedal in order to illicit movement you simply divide the sprocket size by the driver (ie. 25/9 = 2.77). To determine if it’s harder to pedal with a 28/9 gear ratio simply divide the numbers again (28X9 = 3.1111). As we just calculated, if you go up in sprocket size the bike is harder to pedal. Since it’s difficult to pedal you will have a higher top speed but slower acceleration. This falls true for going down sprocket sizes. Lets say you wanted a 23/9 sprocket ratio. The total is 2.55 which indicates that you will be able to pedal easier, accelerate quicker, yet have a slower top speed.
On the other hand, if you change the driver the opposite applies. If one goes from a 9 tooth driver with a 25 tooth sprocket (25/9 = 2.77) to a 25/8 (=3.125) set up, it’s easy to determine you will have a more difficult or slower pedal with the smaller driver.
Dividing the sprocket by the driver size does not determine the exact gear ratio. You must multiply by wheel size in order to do so. However, the method below does provide a consistent and easy way to determine how changing teeth will affect the gear ratio. Use your current set up as a basis for you opinion and keep in mind you may need to remove or add a few chain links upon changing gearing.
If you still ride a cassette you may want a larger gear ratio (ie. 30/9) since you can fakie at higher speeds if you do not have to pedal back as frequent. If you like to ET then you may want to consider having a smaller gear ratio like 25/9.