Both are equally good when it comes to resources or rankings. But, KGMC is slightly better in the number and extent of cases. It is also quite ahead of SMS Jaipur reputation-wise. It is on the way to becoming one of the top autonomous medical institutions of excellence. It is ranked 10th for medical by NIRF 2020. SMS Jaipur is ranked 27 in NIRF 20.
You can even compare the paygrade here to AIIMS. The only other comparable college is AIIMS to KGMC.
I have a few friends at KGMC and they vouch for the college. Based on the interactions I had with them, I will suggest that you choose KGMC.
KGMU Lucknow offers a 2 year Diploma in Medical Laboratory Technician. The eligibility for the same is a 10+2 / a 2 year Intermediate / an equivalent course with Physics, Chemistry and Biology, from a recognized Indian University or Pre-University/Intermediate Board. The admission is offered on the basis of a written entrance test.
If you fulfill the eligibility requirements, you can opt for the entrance test to get an admission into KGMU Lucknow for your DMLT.