Make sure your plants have not been sprayed with herbicides or pesticides before attempting to harvest or consume.
My top four favorite are…
1. Dandelion
Taraxacum officinale
2. Purslane
Portulaca oleracea
3. Lambsquarters
Chenopodium album
4. Burdock
Arctium lappa
As a side note I also enjoy growing Amaranth but I do prefer growing and using the many cultivated varieties as opposed to the wild ones.
Be responsible if you decide to grow these plants as they can spread and some consider them to be noxious weeds. Talk to your neighbors and check local regulations before planting. If you decide to collect wild plants or harvest during weeding be sure that the plants have not been sprayed.