Comparing different concepts should be done by referring to the criteria, properties, qualities defined at the beginning of the process. These criteria can be: strong, light, visually attractive, innovative, entertaining, trustworthy, innovative, efficient, easy to use, recyclable, portable... anything that applies to your product. It can be Emotional or rationaldrivers, refer to real metrics (like liter capacity, speed...) or more subjective grading.
A good way to visualize the similarities and differences is to use a Radar, or Spider, chart. To do so you need to grade each concept regarding the criteria you chose (5-8 criteria). Then you can create the chart, use different colors for each concept the same way it's done on the attached picture. With this kind of chart you can easily compare the concepts regarding each criteria but also the overall difference by comparing areas each concept covers.