I also don't know either one from having stayed at them. But the Quality Suites is on Route 192 in Kissimmee (east of Disney's World Drive and east of I-4 as well) and the Embassy is in the general neighborhood of Downtown Disney (I believe that the hotel is on Lake Avenue before it turns into Sand Lake Road and is quite near Interstate 4). They're probably comparable hotels but Route 192 is awfully busy. Not that you should avoid it for that reason, but when people are heading to the parks or heading home from the parks that route can be slow (frustrating?) to navigate. I always find it easier to get to Disney properties from Lake Buena Vista to the north.
Dick Taylor