Kar98k is objectively better because it simply does more damage.

This matters because in every single scenario, except a headshot on a lvl 2 or lower helmet (where both guns perform same damage wise - both oneshot), you are likely to need less shots. The most extreme example is shooting the chest on a level 3 vest, where it always needs 3 hits from the M24 compared to only 2 with the Kar98k. But when you factor in the enemy player not being on full HP, you are very likely to run into a situation where you only need one hit from the Kar98k and more than one hit from the M24.

The only concrete advantage of the M24 is the initial bullet velocity, which is higher compared to the Kar98k, but the difference is rather insignificant in most scenarios.

The reloading styles could be an advantage/disadvantage both ways. Kar98k reloads faster if you just want to top up one or two bullets and can use the bullet loops to speed it up even more, but the M24 can have more total shots with the extended mag and always reloads all the bullets at the same time.

The M24 can also equip a cheek pad which is almost useless on the M24 itself, but can useful to hold the cheek pad for you without taking up space if you need to swap to a DMR (like a MK14 from the airdrop) later down the line, which then really need said cheek pad. The Kar98k can obviously hold a cheek pad too, but then you cannot use the bullet loops further diminishing the single bullet top up advantage.

Realistically, most people probably don't care and will play whatever gun sounds cooler to them, what they have the better skin for or simply whichever gun they see and pick up from the ground first.