I prefer floorless, mainly for the freedom and flexibility with shoes, dogs cooking etc. In a floored tent you are always cleaning the floor and worrying about the floor anyway.
As for creepy crawlies, I have not had an issue, in fact I often see more bugs and spiders in my bedroom than the tent. I think the floor is generally a faux security, (my kids sleep floorless all the time). Think about it, I've seen more spiders in the house than in the tent. Mosquitos, will get in any tent when the door is open, but once you kill them after closing a door they are generally not an issue. Do you think that a full tent will stop any determined animal from getting at your stuff anyway ? No way. Snakes ? I don't like them, but they don't like me either, as long as you don't set up on snake holes you are good. In our tipi's we have a sod skirt, so I can always flip it outside and cover it with dirt to create a tight seal if I want and then vent the screen door.
The fear of a river in a floorless tent is overblown as well, I've had floored tents where water has come through the floor on several occasions. I've only had this happen once when floorless and it was my fault due to setting up in the "established area".
In dirty sandy areas such as many developed campsites, I prefer a bivy, Bathtub ground sheet, floor, or cot. If I'm car camping I take a cot then I have the advantages of floorless along with cheap hotel comfort. Dogs will get your stuff dirty on a floor, and the same with a bathtub ground sheet. A bivy or a cot will keep you pretty clean. Most backpacking in the NF, I can choose a nice spot.
Not much of an issue