Hakone / Kawaguchiko

I planned to visit Kawaguchiko and Hakone in my upcoming trip to Tokyo in December. If I'm spending 3 days 2 night to do the sightseeing for this 2 places and intend not to change hotel/ryokan, is it advisable to stay in Kawaguchiko or Hakone? Or is it better to spend one night in each of them?
This is my first trip to Japan and will be travelling with my husband and 2 teenage son, your advise is much appreciated.

Hello.
I recommend that you would better stay each city.
It is pretty long distance between two cities and there is not direct transportation between two cities.

In addition to that,Hakone has many attractive spot.

I think you should stay in each city and have enough time to enjoy two cities.

Thanks! If I were to just concentrate on either Hakone or Lake Kawaguchiko for 2 days, which area do you suggest in you opinion?

Hello.

I recommend that you should concentrate to Hakone.
There are many attractions extensively in Hakone.

For example,Ashinoko lake,rope way ,many museums,many onsen,many shops,many restaurants.

On the other hand,Kawaguchiko has good view of Mt.Fuji and lake,but there are not so much more than that.

Do note that the Ropeway is closed because of volcano activity.
http://www.japan-guide.com/e/e5200.html

That said I actually prefer Kawaguchi side of Mt Fuji. Still many things to do on Kawaguchi side.

Hope this helps!!
Have fun!!