Yep, "Best for what purpose". That is the key ingredient. We use different caliber guns for different size game, so we would use different ammunition for different purposes. Unless I missed it, I don't remember seeing WHERE the OP lives. That is important too. Being that I live "One state to the east", I had to change the caliber firearm I use even for deer season because of the large number of bears we have in PA. My 30-30's would have no trouble putting down a PA deer, but if I end up being in the wrong place at the wrong time with the wrong bear even during deer season, I will have a Marlin 336 chambered in 35 REM on the hunt. We have had two hunters that were attacked by black bears in the last few years and in both cases the hunters were injured and hospitalized. So, although I don't feel like I "need" a 35 REM to take down a deer, I want that extra firepower in case I run into the above problem bear.Too many variables to proclaim one 30-30 cartridge is best. Best for what purpose? Best as in what characteristics?
The "best" cartridge in my 30-30, in my current situation, is a hand-loaded Lee C309-150-F, over-top IMR 4064.
The factory cartridges I've tried so far, weren't precise enough. If I were to have found a factory round that was precise enough, (and I am sure there are some that would have been,) that would have been my "favorite."
That choice didn't come from "wisdom.".. and it has little to offer others, since maybe 80% of the other 30-30s may not shoot that ammo precisely.
As long as the rifle/ammo combination is precise enough, the bullet hard enough to hold together while penetrating into the vitals, (probably a non issue,) shot placement does the rest.
...but seeing that I live in Ohio, whereas the 30-30 can only hunt varmints and the like; light, precise, bullets will do.
Now if I lived one state to the east, I would consider using the Lee C309-170-F to hunt black bear.