Roundup kills any weeds and plants growing. Select, poast plus and other grass killers will kill grasses but not any legumes or broadleaves. There isn't anything that kills grasses and broadleaves yet leaves your legumes. There are products like brox, buctril etc that could be used on legumes to kill broadleaves if timing is perfect....during fall dormancy, early spring before legume growth but thats risky for the average person.
Clipping plots before weeds throw a seed head is the best long term solution to weed control.
Note: a healthy soil will have less weeds. Have proper pH and using the right fertilizers for rapid growth will help. Also using cover crops or annual clovers like berseem, arrowleaf or crimson clovers will help reduce weed growth. Radishes, rape and turnips also act as natural weed inhibitors.