Data Foundations emphasizes that "ingest" must produce CMDB data that is standardized, supportable, and upgrade-safe. When introducing custom CIs, the best practice is to reuse the most appropriate existing CI class (or an approved industry-aligned model) and only add what is necessary--this keeps the data model aligned with platform expectations and reduces downstream rework.
Option B supports this directly: the CMDB CI Class Models application is intended to help teams select a suitable existing class rather than inventing new classes unnecessarily. Reusing existing classes improves consistency across integrations, Discovery/Service Mapping patterns, reporting, and CMDB Health rules--reducing technical debt and making future platform upgrades smoother.
Option A is also aligned with best practice when used correctly: once you have the right CI class, extending that class to add additional attributes (new fields) is a standard, upgrade-safe customization approach. It preserves the underlying platform data structures and avoids breaking out-of-box behaviors, identification/reconciliation practices, and CMDB Health evaluations.