Clustered Sequential GUID Primary Key vs Non-Clustered GUID and Clustered Sequential ID Primary Keys
If you're going to use a GUID key, simply use a clustered index with NEWSEQENTIALID() and move on with your application.  The alternative designs are simply not predictably and significantly better when you consider the extra data structures and complexity they introduce.  So while careful testing of your actual application might reveal a superior alternative design, just start with a simple clustered index on a sequentially-generated GUID.
For the gory details on why it doesn't really matter that the GUIDs are generated in the &quot;middle&quot; of the sort order, and the insertion point changes see: Good Page Splits and Sequential GUID Key Generation.