Caliber-kinda depends on your size & strength...for my 6'3 big-boned frame that means a .30-06
for others, a .308...for smaller folks, the other smaller calbers...that's with a B, by the way
Also depends on what you intend to hunt...for white-tail...7mm-08 is great...and low in recoil...
but recoil isn't very bad on the Marlins due to the OEM bedding and recoil pad

.30-06 is quite comfortable,
where on my Uncle's Remmy 700 it felt like a metal-buttplate 12-gauge...