I have never been to Hinterglemm but Seefeld is lovely. It is a really nice traditional village with lots of non skiing activities to do as well as skiing. Only negative is that is a bit lower than other resorts so not as snow sure
We went to Seefeld during Xmas 2014 and the snow conditions were very poor and most of the lifts were shut until Saturday 27 Dec.
Another thing to note is Seefeld is more suitable for beginner and intermediate skiers. If you are all advanced skiers, better go somewhere else. (Don't know about Hinterglemm as we have never been there.)