niether can be destroyed, niether can be penetrated, however the daleks are one of two of the oldests beings of all creation, with power over space and time. they immediatley would resort to biological warfare, debilitating to tripods, no threat to daleks. Daleks will reign supreme! its logic.
A lot of the time, I feel that Daleks may not be the greatest threat in terms of brute force, when compared to other sci-fi villains, but you must remember that Daleks are unalloyed geniuses. If they can't outgun you, they'll outwit you. Unfortunately, the episode "Dalek" was the only one that kinda reflected this.