Do the spark plugs. You will be so pissed off after doing the passenger rear one you won't want to do the O2 sensors.
Be sure to put anti seize on the plug threads, and if the current ones have been in that long, they will most likely very stuck so be careful and hope non break. Be sure the engine is Cold , do not attempt on a warm engine, you could destroy the plug threads.
Now, the O2 sensors, the most important ones are the up streams, they control the air fuel ratio, the down streams are just for cat checking. Spray them with a good penetrating lube, several times this week, and next week you should be able to get them to come out. O2 may not throw a code, but the do get slower with age adjusting, so they probably need changing.