This would go back to the same arguments for any software purchase. My criteria is usually what do you have the most experience in at your shop. Database software at this level is getting pretty generic. SQL Server, DB2, and Oracle do mostly the same things, and generally have their shares of rabid followers. Look around your shop, and if you have mostly SQL experts, then go with SQL. If you have more DB2 expertise, go with DB2. The cost of ownership will be less, if you do not have to send people out for a lot of training, and spend needless hours chasing simple problems that experienced people would laugh at.