The two are in fact the same figure, but with very different color schemes. One of the Aliens vs. Marine 2-packs came with a Night Cougar variant that is also black but with different silver highlights and no red stripes.
Although the Panther/Night Cougar Aliens are very similar to the Runner seen in Alien3, they are likely bigger, stronger and have more powerful claws and tail due to their hosts. Also, they feature a unique bat-like parasite "sidekick" that rest on their back. The parasite (know as "kamikaze parasite") can launch into the air to help the Panther/Night Cougar take down prey with its sharp teeth.