There is not one...
There are several. Need more info. Ground conditions, any rock involved?, sticky mud(gumbo), river rock, red clay, sand, product your placing, are you spot locating.
Best thing to do is cover you ass and have all of them. So here ya go.
1. Sharpshooter fiberglass
2. 6' Sharpshooter fiberglass
3. Trench shovel
4. Rock Bar
5. Sod cutter
6. spade shovel
7. post hole diggers
8. 10' post hole diggers
9. flat shovel
10. jackhammer various bits. Electric
12. pick axe
13. pick maddock
14. Vac Tron (does not work well with rock)
When you find someone actually willing to pick up any of the mentioned tools above use them to work..Please let me know.