Personally, I think a well-lit apartment is a real plus. South, east and west exposures are lovely to live in if you value sunlight (and you have adequate air-conditioning in summer). Right now I have a north-facing studio and I can work practically all day in it. But east exposure might be fine if you work from late morning to late afternoon. West exposure would work if you like to paint early in the day. As long as the sun is not shining directly in you will be okay. If this will be a living space as well as a studio, I think you have to weigh all the factors.