We're strongly considering both, but I voted the tunnel option just so the battle looks a little less lopsided for this poll
I do not believe these options are mutually exclusive and as mentioned because of the ease in blocking tunnels it is almost a necessity that a tunnel bot can climb the bump as well. That said consider that defense played on you while crossing the bump may actually be worse, since an opponent hitting you as you come over is likely to cause a flip, the only advantage is that the bump provides much more room to try to avoid them on the other side.
The tunnel is a good option for simplicity (though keeping a robot under 17" provides its own challenge) and it is significantly easier to move balls through the tunnel than the bump. Defense is easier to play on the platform but from a blocking position the opposing robot (depending on the zone) can do little other than continue to block (center field probably provides the worst shot to either goal in an alliance's home zone, and in the opponent's zone you can't defend many shots from the center either). Although easier I'm not convinced that blocking the tunnel will be very high on any alliance's priority list unless your robot can single-handedly outscore their entire alliance given the chance.