We use the Sapim CX Ray spoke on our wheels. They are the lightest, most aero, and have the highest fatigue rating out of any spoke on the market. With the shape and size of the spoke, aerodynamics advantage is maximized at all yaw angles, whereas larger bladed spokes have a large penalty in any sort of crosswind situation.
We use J-bend spokes on all our wheels which are easily found in most bike shops.
Cycling is a sport done with lots of other people around. There is always a chance of getting a skewer caught in spokes or a crash happening that could break a spoke. Being able to fix something like this with readily available parts (vs. having to wait a couple weeks for a special spoke to arrive) means you can get right back on the bike again.
We use Sapim Brass Polyax nipples in all our builds as well. The Polyax features a rounded bottom of the nipple, this allows the nipple to take on the perfect angle for the spoke to enter. Traditional nipples force the spoke to make a sharp bend as it enters the nipple which can place a lot of stress at this junction. By having this seamless transition, the wheel becomes more durable and the risk of breaking spokes is greatly reduced.
Brass nipples are stronger and resist corrosion.
It will add a trivial amount of weight compared to an alloy nipple, but will make for a longer lasting wheelset that is much easier to make adjustments if needed. Alloy nipples can corrode, especially in areas near the ocean or where salt is used on roads in winter. They are also not as strong as brass nipples which can lead to cracking or rounding off while trying to make any adjustments.
All our wheels feature external nipples which makes adjustments very easy.
With an internal (or hidden) nipple any small adjustments that would be needed would mean you'd have to remove the tube, tire, and rim strip. . .or in the case of a tubular tire completely take off the tire and then re-glue it after making an adjustment to a nipple. One of our goals is to have wheels that can be easily maintained, and internal nipples makes maintenance extremely difficult.