You really make the question difficult to answer in the format it is posed. Lets just say we are assuming that all fuel and tuning requiremnts for both setups are adequate. Also...Turbo is not always on..its more like Nos in that regard. Its there when you put your foot into it a bit....atleast as far as added power is concerned. It all comes down to cylinder pressure. Cylinder pressure = Tq. So look at the Tq output over the useful RPM range. Assuming each one is used the same amount of time at full power..the one with the highest avg TQ output will fail the quickest. In this case most people run an on/off non progressive nos kit will fail first. And we are talking bearings, rings, etc.
But really we are splitting hairs here. I would say only 10% of cars that fail are due to being worn out over time. Most of us blow the motors due to inadequate fule/tune, mistakes, or just plain getting greedy with the nitrous pills or boost controller. Usually resulting in detonation or just plain exceeding mechanical design limits

How many people with turbos or nitrous run at a medium safe level. Not many...most are pushing their setups to run right at the limit 95-100%, with almost no margin for error. Thats the human factor . The human factor results in more blown motors than any differences between N20 and Turbo.