Both areas are good. The nice thing about Powerhouse District, IMO, is the variety of transportation options. The Light Rail opened up the western side of Hoboken, but still has only one PATH Station, and it's located in the southeast corner. The Powerhouse District of Downtown is in a great location, where you can walk to 3 PATH Stations. Hoboken has some charming neighborhoods of brownstones (as does DT JC.) For anyone wanting spacious, loft condos AND a convenient location, it's hard to beat the PowerHouse District.
I'm not sure what you meant by "investment". If you want to buy to rent, I'm not sure either is a great choice.