Comment by bluGill
Spouses always get better treatment as there is a voter who would be mad otherwise. They check for scam marriages but otherwise hurry the process through - if they don't a voter contacts their congressman to push the process. That voter will also likely know a lot of other voters and thus influence the next election while someone not married is unlikely to have that local network to use.
This is patently false for one reason - once someone has a U.S. green card and has met the residency requirement to apply for citizenship, the application form and process are the same for everyone, regardless of how they got their green card (through work, marriage, asylum, investment, etc.).
Once you are eligible to apply, the whole process is basically form N400->biometrics->interview (just doublechecking your name and other paper info, takes 5 minutes)->civics test->ceremony.
However, the timelines and process for getting the green card itself is different depending on the nature of your visa, and they will indeed try to check for scam marriages before you get your green card (if you were applying for it through the marriage visa).