Which of these is better in IIT Kanpur: BSC in Chemistry/Physics, Earth Science, Biological Science or Engineering?

It depends on what you are interested in and what career you want to pursue. My personal suggestion would be to make IIT Delhi your first preference.

First, if you are a civil services aspirant, get admission into IIT Delhi in any branch and prepare for UPSC through the various coaching institutes available.

If you are somehow not able to make it into IIT Delhi, then invest another year preparing for JEE and aim for a higher rank. Once you are able to make it into IIT Kanpur, again you need to work hard for one year to get a branch change into Civil. You will be competing with geniuses from CS and ME but keep yourself motivated. A CPI of 7+ will make it possible to get a branch change. Attend your classes regularly, complete your assignments on time and you are good to go.

Lastly, if you are unable to change your branch, go for pure sciences like Physics, Chemistry, BSBE, or Earth Science. Out of these Physics and chemistry have a heavy workload and it will be tough to cope with your batchmates. BSBE has pathetic placements. Another option is Earth Sciences which in my opinion is the best considering the light workload and job opportunities. The average CPI is lesser than other branches and most of its courses overlap with Civil Engineering. Basically, Earth Sciences is equivalent to Civil Engineering just without the Engineering element.