For me, it depends on the tank, for high tech, and if you can get the conditions right then Hemianthus callitrichoides 'Cuba' is a major contender, although I'm also a fan of glosso and hairgrass works well.
For low tech tanks hairgrass can be a bit sparse and look a bit lost. Pogostemon, as you've pictured, I've found grows ok in small clumps but doesn't grow in the carpet like you have pictured. However options like staurogyne repens, e tennelus or some of the smaller crypts or saggitaria make a good option.
I'm not a huge fan of attempts at moss carpets, it doesn't really like to grow that way in my experience, and never really looks happy as a carpet.
RIght now I've been looking at using Marsilea in a set up, also a lovely plant, but I have a propogator full of lilaeopsis, which will probably end up going in as I already have it.
hmm this is a hard one i don't think i have a single fav but i do love DHG and I'm trying to grow it in my current tank it is slowly getting there but i do love crypts and my tank is mostly crypts at the moment