Although physical appearance may count, it is not really the thing to put top of the list when choosing a DP. You need to decide what features or functions are important to you, then get someone to help you choose based on the keyboard touch (both the models you mention are likely OK), sound if you will use the inbuilt sounds, and features you want and will use.
Of the two you mention I would choose the CS7, but others might choose the 505. I chose neither for myself. Both are good but do they fit your needs, and do they speak to you?