My data is not the latest (around 1+ yr plus ago), but D cube has excellent service and Plat recognition, while Chosun's location is excellent (recognition wise- well expect less, and you will not feel so bad.)
So all depends on where you want to be, the prices for your dates.
If you want to be in Myeondong, visiting Namsan, or going Dongdaemun, Chosun's location is fantastic.
D cube's location is off, but I guess if you are visiting the fish market, or going to the financial centre, then it is not too bad.
Gangnam wise, both are not exactly that near it, so I guess if D cube has a good price over Chosun, maybe.