Do you mean long exposures, or hand held available light photography? The ideal films for each are very different. Speed is much more important for hand held photography. And reciprocity maintenance is very important for long exposures (to make them much less long and much more predictable). Delta 3200 is the fastest b/w film, but it is a vile offender in the reciprocity department, once you start shooting long exposures. OTOH, Acros and T-Max are the best in terms of reciprocity, but at just over three stops slower than Delta 3200, they are not generally fast enough for hand held low light photography.
Thus, for long exposures, I would recommend Acros or T-max 100. They have the best reciprocity during long exposures, and have a lot of latitude. For color negative film, I would track down some Portra 100T or Fuji NPL (both discontinued years ago). For color transparency film, I'd use Provia or Astia. They have great reciprocity characteristics in long exposures, though you will probably need to filter them more heavily than the tungsten-balanced negative films I mentioned, if you are shooting in the city.
For hand held available light photography, I would use Delta 3200 (which is an ISO 1000 speed film) or T-Max 400. I'd use the Delta to get the highest raw film speed. I'd use the T-Max for flat lighting only, unless you want extreme contrast when you push. It is also incredibly finer in grain than the Delta 3200. As for color films, try to find Fuji Superia 800. They made a 1600 too, if you don't mind large amounts of grain. The 800 looks much less grainy and more sharp even when pushed, but the drawback is the loss of the shadows. I think the 800 is still made, though it has been discontinued in pro packs. I am pretty sure the 1600 has been discontinued, or maybe it is no longer shipped to the U.S.A. For transparency film, Provia 400X is it. It's daylight balanced, though. It is a real shame that there is not a tungsten-balanced version.
