A 30-30 is is going to be a more rare rifle of the two calibers. I am no expert, but even an older 99 should be able to hold up to most if not all 30-30 loads. The 99 in 308 would be nice as well, but my self I'd opt for the 30-30 since I never seen one.
I own a 99 in 300 savage, love it too...