If you had to pick one of the major cities as being the most important, which would you choose?
For me it would be Whiterun

Whiterun..but solitude is also a really cool city

I like both Whiterun and Windhelm (slightly prefer Windhelm because it looks like a might fort and Whiterun is a little too "edoras" for me)

haven't been to Markarth, Riften or Solitude yet.

As for the smaller cities, only been to Winterhold yet, which is smaller than Riverwood I think. The college there is nice

Whiterun is seriously biggest city in the game? I thought its rather small... In comparison to Imperial City in Oblvion, Whiterun is really small

markath has some pretty good quests and is almost as big as whiterun I think.

I've heard Solitude is the biggest city

All of the cities are about the same size in terms of building count, Windhelm is probably the biggest in terms of area. This is one thing I'm really dissapointed in, I know I've hammered on about how much I want bigger cities, and indeed they are much more elegantly designed than Oblivion, but they are SO [censored] SMALL it really bugs me. They are smaller than Oblivion cities, which were in themselves basically villages. I mean there's barely a house that isn't a shop or a chapel/shrine or a house of the dead in Skyrim. I think there's about 18-20 buildings in a city. EDIT: It is apparently illegal to wish something to be damned by God even in the nonliteral sense on these boards.