Honestly my tractor tools evolve from my needs as I'm using them.  When I need something I don't have it gets added.  I prefer Snap-on, I have a 3/8" ratchet in my pickup toolbox I bought in 1974 when working part time at an Oliver dealer while going to school.  I decided to splurge this summer.  I saw a Snap-on truck at a shop and bought a 1/4" ratchet.  I should have asked the price before saying I wanted it. At about $125 it will probably wait another 50 years before I do that again.

For tractor use I generally go to Rural King, Menard's, Harbor Freight, or Wal-Mart and shop sales.

I recently loaded a new service truck with tools (mine was stolen).  I went to Harbor Freight and bought everything ICON if possible.  Not that they are better than anything else but the they are reasonably priced, do what I want, and most importantly the only place on the farm you find an ICON tool.  If I find one it gets put back in the service truck