In a straight stuck in an areana style battle, I think it would come down to Jake vs Rachel, I think a Siberian tiger could take a grizzly. Siberian tigers hunt brown bears (although not grizzlies) as an alternative food source. Siberian tigers have an average weight b/w 450-600 pounds. And are extremely fast and agile.
The average weight for a Grizzly is about the same, between 400 and 600 pounds. Grizzlies are also fairly fast in a run, but not as agile.
They both have very similar weapons, but I believe the tiger could use them easier than the bear because of it's agility.
Now if Rach had a kodiak...
also the terrain would matter, if there were things lieing around that could be used as weapons, like logs or big rocks, I bet Marco would put them to good use, and he'd be the only one who could.
Now in a scatter battle, I think it'd be either Marco or Tobias. They both have the right mentality for that kind of fight. Both would be able to operate alone fairly well, and have the sense to stalk a target and know to wait for the right moment to strike, don't forget that Tobias has a Hork Bajir he has used effectively in fights and Marco has a cobra, pretty close to a one strike weapon, but in a scatter battle that's all he'd need.
Now if they were already morphed, I think Jake could handle Ax, or at least make it an even fight, it was mentioned a few times that his tiger was fast enough to avoid V3s tail in a few fights