I have a couple corsairs,and think they are great.the drag is as smooth as you can get.As with the other 7 or 8 shimanos of different types I have.I don't think you can beat them for the price.
I had a couple ambassador 5500s and don't care for them any more.They use to make an excellent reel but think they just arent of the same quality the last 3-4 years that they used to be.
The Quantums I think are made by Zebco.That should give you an idea of the quality there.I havent used them personally,but a friend of mine bought one for plunking.No matter how tight you set the drag you could watch your spool back off and feed line.He took it back and got another.It did the same thing.Thats really the only experience I've had with them.Didn't want any more.