Well there shouldn't be much difference in appearance between the VS2 and the SI1; both should be eye clean! You might be able to see the difference in H and the I color diamond, but I seriously doubt it! However if one of these diamonds has medium or stronger flourescence than it will appear much whiter, possibly 2-3 color grades. So if the I has flour. go with it and keep the clarity otherwise go with the one that has the best cut! I notice you didn't specify the shape but the proportions of the diamond will affect the beauty of the diamond more than any other factor! For example a J SI2 ideal cut will look much better than and ordinary cut D FL round. Of course I'm sure you already know this.
Jackie S