Despite this advantage, butted spokes don't enjoy great popularity. Aero spokes, like aero rims, offer a small decrease in wind resistance that is mainly of value to competitive cyclists. First, in almost every case, the aero spoke must still fit through the hub flange, which means it cannot be very flat. Second, the less round the spoke, the more easily it twists during wheel construction. That's an aggravation.
Most riders find their needs best filled by standard, round spokes.
After you've decided on hubs, rims and pattern, your source for spokes should be able to determine the spoke length you require. If not, try to find Sutherland's Handbook for Bicycle Mechanics. It's just that small-flange hubs do the job well enough, and the amount of extra strength afforded by large flanges isn't worth their extra weight. One conspicuous exception is track racing, where large-flange hubs are still practical and popular. When choosing among small-flange hubs, weight is a relatively minor factor because most models are of similar size and their mass is concentrated close to the wheel's rotating center.