I would have to say go with Oracle. There seems to be more limitations from SQL Server. These are based on known issues from Microsoft rather than issues with Maximo. For example:
1. Fulltext Search in MS SQL Server - Maximo makes use of the fulltext search feature in MS SQL Server. MS article 910067 report database restoration error when DB is with FullText.
2. Clustered index - it is noted that the database design does not make use of Clustered Index feature (by default) in MS SQL Server. Not using
clustered index will result in the documented bug to happen. please refer to MS article
http://support.microsoft.com/?id=913399 regarding this bug.