Ryan H. (eldeeem) has been investing in a lot of Modulex lately. He says it is perfect for making mosaics based on square pixels. Here he shows us an example with Sonic the Hedgehog.
Modulex has a different size ratio than regular LEGO bricks. A Modulex 1x1 brick really is a cube, unlike the standard LEGO 1x1 brick, which has a dimension of 5x5x6 half-plates. Modulex dimensions would definitely make it easier to construct SNOT-y mosaics (with the studs pointing to the top, instead of outwards). One other interesting aspect to Modulex is that it comes in different colors, as you can see in Ryan's chart here.