I haven't a clue what you're talking about

I am making a border of either mondo grass or liriope, in fron of thsee hydrangeas. What looks better.

I have a lot of verigated liriope in other areas so it would be natural to add more of that, but I'm concerned the purple blooms will look funny in front of blue hydrangeas, which is why I am also considering mondo because it does not bloom and just acts as the from border. Need opinions

I am not a fan of borders. Much better to use a groundcover.

You mean something like a hosta or like a creeping jenny type cover ?

I had thought about alternating between the liriope and hydrangeas too..

Some people like a row of low stuff at the front of their beds.

I have lots of black mondo grass and it looks great with hostas- the contrast in color and texture works well. The blooms on the grass are small, unobtrusive, and don't last long. Liriope if you want taller or mondo if you want lower.

IMO you need some shrubs and small understory trees back in there to give you some height. All low plants against that stark fence might not look as good as you anticipate. And the foliage would screen those neighbors.

I think the best ground cover is more hydrangeas. you can layer them, with dwarf types under and between the ones that will eventually grow tall and wide. Many of the serratas work beautifully and that is what I do. I also use Brunnera, Heuchera, hardy gingers and ferns. There are small ferns that have beautiful contrasting foliage and don't forget Hellebores! Your list could also include saxifrages - but check their growing zone or check in neighbors gardens. Rather than borders - think ground covers.