Never been to Amsterdam apart from the Airport.
Berlin is awesome however. Don't know much about hotels we rented an apartment for the weekend when i visited about 5 years ago.
i recommend visiting;
en.wikipedia.org/wiki/Kunsthaus_Tacheles
this is a squatters resident from when the wall fell. It has about 5 bars in it, including a roof top one and a slightly blade runner esc red bar. It also has art galleries and a cult cinema.
--- apparently the artists have now been evicted after 22 years so this might no longer be somewhere you can check out.
Not sure if your into night life Andy (btw i went to Berlin on a stag weekend) but if you are i recommend either Weekend Club,
www.week-end-berlin.de/
, or Berghain
berghain.de/
. Weekend club is on the 14th floor of a soviet towerblock so you get a good night view over the city. Berghain si probably the best club i've been too. Its very weird, lots of strange night people there, no cameras are allowed and the door policy is one of random refusal. I got in at about 2am and stayed until 8am when i was there, it closes at bout 6pm sunday eve. Theres a room where people can sleep or do other things. Lots of industrial techno. Its built in a decommissioned coal power station.
other than that theres a bunch of war stuff, the wall, the holocaust memorial, and a bunch of museums.