The CCA of batteries varies from one battery to the next. Normally the higher CCA the more the battery costs. Just buy one that is at least as big as the OEM battery.
The 12 amp hour battery will last longer under the same load as a 10 amp hour battery. For example if you had a load drawing 2 amps, the 12 Ahr battery would last 6 hours and the 10 Ahr would last 5...