What are the sizes(ingame) compared throughout the Elder Scrolls games.Heck maybe even compared to Fallout games.I know that Daggerfall is the largest and that's about it.How big are the areas in square kilometers or miles.Also,which do you prefer, more size and less detail, or more detail and less size, or maybe both?

Daggerfall does not really count. All the map content was dynamically generated or randomly generated. There was no walking between places, FT was the way to get around. Yes, you could walk, but you went through a pretty blank world space with little in it to see, except maybe enemies who were out of site but could hit you with arrows. I walked to a place once in that game, never again. It was bad enough in the endless cities trying to find things.

Back to your question:

For all the other games, the maps have been big enough for me. I don't like walking for walking's sake, see above. As long as the places are not crowded on top of each other and there is some distance between them, then the map is fine. Maps in these games are really just there to keep all the places you go to from bumping into each other. The worst game in the world would be the one that has a realistically scaled map.

I'd like a Skyrim like map(I found the mountains and everything else perfect, but the cities and landscape and ammount of dungeons and dungeon sizes and NPC's increased 3x.

The size of the world is really debated, but from what I've heard Daggerfall was a couple hundred thousand square miles, although it was randomly generated so it was very bland. Morrowind was supposedly around 4 or 8 square miles from what I've heard, and Oblivion and Skyrim were both 8 or 16 square miles, although again, these could be wrong.

I personally prefer a bigger world, but not too big-I think Oblivion had a great world size, although I would like to see it a little bit bigger if they could keep the amount of detail they have, because although I love having a big world, it needs to be detailed.

I could roll with that. no need to increase the Dungeon number drastically though, Increasing the landscape size would just mean that you wouldn't find a dungeon every 5 feet