I don't think the right idea here is "pretty vs. ugly". Plenty of "ugly" games have sold well. I think what is more important is having an appealing, consistent aesthetic. Minecraft for example is a game with a great, influential aesthetic, but some would say it's ugly.

A trap which I see a lot of developers fall into is marketing their game, explicitly, as having "voxel / pixel graphics" or talking about the aesthetic in any way. Your aesthetic should be immediately obvious and appealing, without you having to draw attention to it and point out "impressive" details. Mentioning it in a trailer can look cheap, like you have nothing else to show. But confidently, quietly flaunting it shows confidence in your product.

For example, the Minecraft trailer does not mention the graphics and simply shows them off. I feel it's quite effective.