Hi Shriniwas,
You might be aware C_HANAIMP141(SPS07), C_HANAIMP142(SPS08) both are dated 2014
C_HANAIMP151(SPS09) is dated 2015(so it does not correspond to SPS11)
Please find some information on differences between these versions in the below blog
http://scn.sap.com/thread/3828831
As far as the latest version of the Certification is considered SAP has not introduced any newer certification for SPS10 that corresponds to C_HANAIMP151(SPS09)
Instead SAP introduced a D_HANAIMP_10 that would be a differential of the new topics that have been introduced in SPS10 and need C_HANAIMP151 as a pre requisite, please refer below link for more information
http://scn.sap.com/docs/DOC-61609
At any given point it is advisable to go for the latest version of the Certification
With HANA evolving every year SAP has been keeping a validity upto the last 3 versions, so the version C_HANAIMP141 could become invalid soon(going by the trend it could be in next 6 months or 12 months(best case)) and there is no possibility to attempt D_HANAIMP_10 to be able to upgrade to the latest
In such a scenario the recommendation would be to try and attempt C_HANAIMP151(as you will have an opportunity to upgrade to D_HANAIMP_10) unless validity is not a concern
Hope it helps
Sunil