shabbat - Pikuach Nefesh on Shabbos priorities: efficiency vs transgressions

When in a life-endangering situation on Shabbos,
what takes precedence - efficiency or amount of transgressions?

For example:

• in Jerusalem, one can call an Arab taxi driver and wait for 5-10 min or use a Jewish friend with a car


• a Jewish nurse can use a regular stethoscope or a computer scanner


• in the emergency, there are two operating doctors: a Jewish professor or an Arab stagiaire