Hi Joe,
My personal opinion is that you should go for C_HANAIMP131.(if you are really interested in modelling)
SAP has come up with lot of new content in that certification, especially in the Data provisioning side.
C_HANASUP_1, relatively being mostly into support, am not sure how much useful it would be for you.
Since C_HANAINP131 is relatively new one, I am not sure if you will find lot of helpful inputs.
But you can go through the following document where I have tried to include many useful links(examination point of view)
http://scn.sap.com/community/developer-center/hana/blog/2013/12/16/my-hana-certification-chanaimp1-experience
BR
Prabhith