I strongly recommend which ever on makes you happy, but I consider the 7x30 a better choice in the contender, regardless of barrel length. As noted above, factory ammo, factory brass, better bullets in 7mm for this type of hunting gun, more up to date loading data as newer powders come out and finally, with proper loading, the 7x30 will give you about the most you can get out of a contender without using a 444 case.
regards,
Graycg