Oracle Teradata comparison:
Exadata is still Oracle:
http://www.teradata.com/t/white-papers/Exadata-the-Sequel-Exadata-V2-is-Still-Oracle/?type=WP
Exadata is still more Oracle:
http://www.youtube.com/watch?v=25gV37PfYuY
Teradata to Oracle migration:
http://www.oracle.com/technetwork/database/migration/teradata-089107.html
Oracle to Teradata migration:
http://www.teradata.com/data-warehouse-migration/oracle-migration-services/
Migration from Oracle to Teradata:
http://www.teradata.com/podcasts/Migration-from-Oracle-to-Teradata/