You are going to have more range/distance capability with the 7x30 Waters and or the 30-30 than you will with revolver cartridges.
Is that important for you?
The rifle cartridges will also shoot flatter, since they are lighter in weight and have a higher BC (More aerodynamic).
The revolver bullets will have a larger diameter.
It really comes down to preference-Your preference.
How far would you like to be able to shoot and practice at?
By nature, do you prefer straight wall cartridges over bottleneck?
Do you intend to reload, or do you strictly want to purchase ammo?
How much will the ammunition cost and how available is it?
How recoil sensitive are you?
With the Contender using the 30-30 or the Waters, I would suggest the 125 NBT for the 30-30 and the 120 NBT for the Waters, IF you choose to reload.
I have no recommendations on factory ammo, since I rarely use it.
Ok what factors should I weigh to do that? Plus and minus.