Both of these guys aren't making the team - if they were to go short at positions like safety, wide receiver or linebacker, they would be losing a guy who can contribute on special teams for a player who won't make that type of contribution.
While Gardner has a great motor, leadership skills and brings the kind of intensity and effort that can be infectious on a team, he is a limited player both physically and positionally. His arm length, or lack thereof, will always be a problem for him out wide, and he's too small to play inside. Russell physically has much more potential, and is demonstrating the ability to play multiple positions. I don't think that either would be primed to make much of a contribution this season due to the players in front of them, but I think that Russell's physical/positional gifts will win the day.
Gardner will be a cut, and will catch on somewhere else. I could see the Bears wanting to take a look at him, as Vic Fangio was his defensive coordinator at Stanford.