Since the question is "who's a better rapper?" Doom without question. If it was who's a better rapper/producer that's a better question and I could see an argument for RZA at his peak, RZA produced some really dope songs for himself and his solo catalog actually has a lot of heat.
No way in hell is RZA fukkin with Doom as a rapper though.
I love Doom but give me a verse that’s competing with this
“Fusion of the five elements to search for the higher intelligence
Women walk around celibate, livin' irrelevant
The most benevolent king, communicatin' through your dreams
Mental pictures been painted, Allah's heard and seen
Everywhere, throughout your surrounding atmosphere
Troposphere, thermosphere, stratosphere
Can you imagine from one single idea, everything appeared here?
Understanding makes my truth crystal clear
Innocent Black immigrants locked in housing tenements
Eighty-Five percent tenants dependent welfare recipients
Stapleton's been stamped as a concentration camp
At night I walk through, third eye as bright as a street lamp
Electric microbes, robotic probes
Takin' telescope pictures of the globe
Babies gettin' pierced with microchips stuffed inside they earlobes
Then examinated, blood contaminated
Vaccinated, lives fabricated
Exaggerated authorization, Food and Drug Administration
Testin' poison in prison population
My occupation to stop the inauguration of Satan
Some claim that it was Reagan, so I come to slay men
Like Bartholomew, 'cause every particle is physical article
Was diabolical to the last visible molecule
A spaceknight like Rom, consume planets like Unicron
Blasting photon bombs from the arm like Galvatron”