These days, cars are built to be very reliable irrespective of the powertrain and reliability also varies from manufacturer to model wise too. Speaking generally, a modern diesel engine is very reliable, however its long term future is uncertain with all the negativity around the fuel and its environmental impact. EVs are also reliable given that there are far fewer moving parts, battery life too is long and most brands now offer warranties in excess of 7 years to even lifetime (15 years) warranty.
However in the long run an EVs resale value is yet unknown. Thus looking at reliability, and a long term service life a petrol is a safe bet. The engine is reliable and easy to service with much less complexity than a hybrid.