As a general rule of thumb, COB LED lights are higher-quality light sources. That’s because they use reflectors to provide focesed and controlled light. In addition, they don’t feature the frosted lenses that come with SMD LED lights.
COB LED’s are known as a higher-end LED which gives off more of an architectural look, if you intend on living with your LED downlights long term then look to a COB, if you are installing in an investment property then SMD will do the job.