It really depends on the species you are tyring to kill.
Garlon or Tordon do a good job on most, but there are some species that one will kill and the other won't... Look at what most of your targets are, and get whatever will work on that. Here is one publication I know of showing what works on which species (for Ohio species): Link to pdf file from Ohio State
I will be cutting out (not drilling) some large holes in low/near ground grade stumps left from last year
as well as some new oak stumps for trees soon to be cut.
I am leaning toward trying high nitrate fertilizers or saltpeter / nitrate of potash- the main ingredient of some stump removers - to put into the large cut out stump hole.
Also wondering if cheap ammonia could also be possible.
I have found MCPA Dicamba works well for Willows Poplar or stump/root suckering types like Robinia. Just drill n fill stump or spray the suckering leaf (at the right time). You can/may/if want to control root suckers of above with a gentle weak leaf spray without killing the host if used with care.
Its a lot $ less than Garlon.
Quote of the week for working with chippers.
Never put your hands in where you wouldnt put your D**k