For any application where run time is important (outdoors, emergencies, auto, etc), the Gerber will be the much better choice. The Streamlight is a great light, but I find I don't use it as much as I could due to its short battery life. It is incredibly bright and powerful, and really impresses the heck out of Mini-Mag folk, but it may not be practical for all uses.
If you need a brighter light for brief periods of time (or if changing batteries every 90 min. is not a problem), then the Streamlight Jr. is great.
If you do not need as much light but changing batteries frequently is a hassle or concern, I would not choose the Streamlight.