In .30 caliber I have killed deer with my 30/30, .308, and .30-06's. For whitetail hunting I choose more by which gun I prefer and what scope is on it, because I have had good success with all three. I think the 30/30 is a great deer cartridge, more overshadowed by the relevancy of opined comparison than its real attributes and ability to disrupt a deer's anatomy. The 30/30 has been around for a long time, in many cases it was a youngster's first deer rifle until he "graduated" to something more powerful. And while the 30/30 has been around there have been a zillion newer cartridges introduced that were faster, flatter, and what all. Meanwhile the 30/30 has continued to pile up a lot of venison. All I know is that the deer I have shot with a 30/30 were just as surely dead as any I shot with any other cartridge, and I have never lost a one.
I have friends who are experienced hunters and good shots that often talk about how they like their game to die in a split second and hit the ground like a ton of bricks (my words) and indicate their suspicion, or lack of confidence in something like the 30/30 as compared to their .25-06, or 7 mag, etc. that just "knocks 'em over" on the spot. If you shoot a deer through the heart, and just destroy that heart, it is not uncommon for that deer to run 75 yards +/- before piling up stone dead. Actually, they were "dead" before they even started to run. What more could you ask of the cartridge? I am mostly a heart - lung shooter who waits for my shot. I think if you never want the animal to move after you shoot it, you have to compromise the nervous system - which you can do with a 30/30 as well. The longest shot I have made on a whitetail was 165 yards, which was a one-shot (heart) kill. I have confidence in the 30/30 - pick your shot, use the right bullet, put it where it belongs. Like a guy once told me when I first started hunting - " A gut shot deer with a .460 is still a gut shot deer."