Floor! Because most places I tent out west have no or very little grass. A floor will matt down tall weeds and keep the dirt out, especially when raining...nothing like a stream running under your feet!
Mice will be mice with or without a floor.
I’ve been sleeping in both floored and floorless tents in the west for about 35 years and did it year round for about 8 years.
My experience is that throwing a tent with or without a floor over tall weeds or any vegetation without a little site prep makes for pretty uncomfortable sleeping. Now that I’m older, it also makes me stiff as a board on the morning even with the glampy sleeping pads I tend to use now.
On the subject of dirt, it really depends on the soils you’re dealing with. But if your on sand or if you have high winds, you’ll have dirt all over everything in either tent.
Like others have said water, ice and mud, is where floorless tents with a wood stove really excel. You can dry it out. You can’t do that with a synthetic floor. And I’ve had water running under tents with floors. A stream you can avoid by where you pitch the tent. The times where it happened to me, it was sheet flow from big storms. It sucks in either situation, but I’d rather have it happen in a floorless tent with a stove by far. Way easier to get your shit dry.
Finally, I think most people feel uncomfortable sleeping in tents without a floor because of the potential for critters. I’ve spent hundreds of nights cowboy camping on the ground in the west without a tent, generally on or rolled up in a tarp or ground cloth. I’ve never had any issues with critters… On second thought, I do remember finding a scorpion under my sleeping pad once when I was sleeping on the dunes in White Sands National Park. He didn’t bother me.