Which Mid and Small index fund to choose?

I am thinking of investing in the midcap 150 index fund and smallcap 250 index fund. I have short listed some funds. but ocnfused to which one to select. on one hand I have fund that has good AUM and are around for 5 years, but has higher expense ration. while other funds are new and has lower AUM but has lower expense ration. here is the list. can you help me decide. also please consider the tracking error part too. 1. bandhan nifty midcap 150 index fund - 20 cr AUM. expense ration 0.21 2. Edelweiss nifty smallcap 250 index fund - 99 cr AUM. expense ration 0.13 1. Motilal oswal nifty midcap 150 index fund - AUM 1980 cr. expense ration 0.30 2. Nippon india nifty smallcap 250 index fund - AUM 1900 cr. expense ration 0.35