It's always many plants togheter. It's a humid climate here, I planted few roots of mint in couch grass here and there, also some wild strawberries and other plants. I let couch grass growing and later pulled it out. Better uproot with stronger plant. Also soil got loose and mint and other plants could grow. On site where there was mostly grass before, there are now wild strawberries, parsnip, cumin, horseradish, fruittrees, clovers, other plants, mint inbeetwen and only few couch grass.
If you are looking for one plant, i would say mint. Next to above place I planted potted mint with strong roots in the middle of grass and it's a big circle of mint after two years. In this way of planting with strong roots it can be a great barrier for grass. Once you plant mint, use it in various ways, that way you don't let it grow to much where you don't want it.