I had virtually the same dilemma back in 2010 when I decided to get my first train set and I settled for 7939. As the other have said, it is a very good choice for a start, with points, lots of straight tracks and other stuff, even if a bit pricey. And the engine looks great when hauling either cargo or passenger cars.
However, if money is no bigger issue, I would also recommend what one of my fellow AFOLs once mentioned: get yourself two 7938s and Maersk/Horizon. The benefits you get from all those are:
- two full circles of curved tracks which are currently not available in track sets
- two extra passenger cars from second 7938 - one original and one MODed from the engines
- motorization for Maersk/Horizon from second 7938
- full Maersk/Horizon