Should I join IIM Indore this year or take another shot at the CAT?

You have not mentioned your profile so it’s difficult to answer precisely. Let’s assume you are a male IT engineer with decent academics.

Your decision is solely based on your profile. For instance, if you were previously earning 12 LPA in your job and are content with it then you may go for a year drop. Or if you wish to convert to better colleges in this league such as IIM BLACK or XL or FMS, then keep in mind that the selection criteria of IIMs are very unpredictable. 

The previous year, GEM at 99.3 was converted at IIM K easily. But this year the cut-off for shortlisting of IIM K was 99.8+ with good academics for GEM. Moreover, your decision depends on the branch you have converted. Compare the previous placement records to have a better knowledge of your choice. You should not negotiate with your course of interest.