I have gone to Genesis twice, once for a 90,000 mile major service and once for a clutch which failed and rended my car inoperable. Both times, the work was done well at a good price and with little or no advance notice. Both times, the bill was lower than the estimate that they gave, and they never tried to do any work other than what I brought the car in for. When they replaced the clutch, they showed me the failed component and explained what happened. In my experience, the mechanics at Genesis are honest and do good work at good prices.
Service is of good quality but can sometimes feel impersonal and overly bureaucratic.
Marco's offers prompt and excellent service. The customer service is superb and personal, and the cost reasonable. They'll often tell you if your car looks like it needs any more serious work. They are pretty cool people when you need help. They even stock engines.