Rim weight, because it is an easily obtainable number and it correlates quite well with important factors such as cross section and wall thickness, is still your most reliable and accessible indicator of rim strength. Aluminum rims are the only type worth considering when performance is a concern. As opposed to steel, aluminum is light, can't rust, and offers vastly better braking in the wet. The world of aluminum rims can be divided in terms of the two tire types, tubular and clincher. Compared to clinchers, they have little to offer those who ride for recreation, fitness, touring, or even most types of racing.
Tubular rims are a different story, however.
The lightest models can reduce the rotating weight of a pair of wheels by as much as half a pound compared to the lightest clincher rims. Rotating weight is very important because the greater it is, the greater the amount of energy required to change its speed. This is critical in criteriums or any other event where there are many accelerations and other adjustments to speed. A lighter wheel is simply more responsive. Unfortunately, it is also less durable.