depends on what u mean by braking efficiency and how you'll be abusing the car.
Drums
pro:
very efficient & fast at converting light braking pressure into large braking force due to its inherent "self-exciting" engagement, where the motion of the drum wedges the shoe harder and boosts braking. that's the main reason why there's a "load sensing brake proportion valve" at the rear to delay/limit the rear drums to allow the fronts to lock first before the rears during emergency braking.
also the reason why the handbrake is much more powerful on drums compared to discs.
being more common, there's alot more spare parts available at lower cost compared to rare rear discs.
con:
limited heat capacity due to lack of cooling in the enclosed braking system so it quickly looses efficiency / fades once too hot after afew repeated/constant hard braking with no cooling period (ie high performance driving on/off circuits or heavy prolonged downhill braking with full load without engine braking)
exposed self-adjuster threads prone to brake dust contamination so it seizes n degrades the handbrake range if not maintained.
Discs
pro:
high heat capacity so its more resistant to fade during heavy abuse (ie high performance driving on/off circuits or heavy prolonged downhill braking with full load without engine braking) and provides a more consistant efficiency range
con:
very low braking efficiency, requires high braking pressure for a low braking force,
the old "load sensing brake limiter valve" that nissan left on, reserved for the common drum brakes ain't helping rear braking with these inefficient rear discs (I fitted a manual bias valve),
handbrake is quite weak compared to drums,
handbrake mechanism inside caliper also tends to dry/seized with age and is much harder/expensive to service due to special tools & being quite rare so spare rear calipers n parts become a premium.
imo for public roads stick to drums, for intense motorsport abuse discs are more versatile.
swapping to rear discs require:
finding a rare rear disc axle or modifying a drum axle to support calipers,
new trailing arm and bolts cos the old one's are most likely fusion rusted in place n require cutting out,
new discs & pads always advisable,
left & right handbrake cables,
caliper brake hoses,
always highly recommended for old used rear calipers to get checked & serviced for rusty pistons or seized handbrake mechanism so potentially require a rebuild kit,
and more brake fluid.
