I'd rather see people giving reasons...
In the TCG, Metagross is a Stage 2 Pokemon. Unanimous victory.
In the game, both have different roles.
Bronzong can be a top Wall and an Annoyer, because it's so annoying with its type and either Levitate or Heatproof. Confuse Ray on a Bronzong really pisses EQ-ers or Fire Sweepers off. It also has high defenses and its type, once again, makes it hard for even good Sweepers, both Physical and Special, have a hard time taking it out. It's slow Speed can take out many fast sweepers using Gyro Ball.
Metagross makes an excellent Sweeper-Tank, as its type and defense stats are decent enough to sustain at least one or two hits from a hard-hitting Sweeper. It also has very high Attack, but a little too slow to be a Physical Sweeper. It can learn Magnet Rise in DP, which removes its weakness to Ground temporarily.
Now, as for pitching these two against each other, Metagross has high-enough Physical Attack to get rid of a Heatproofing Bronzong using EQ. If not, Metagross can use Thunderpunch (from 3rd gen) all the way, which will take a long time. On the other hand, Bronzong's stats will not be high enough to deal decent damage against a Metagross as Bronzong can't learn any Fire moves and its Attack base stat is 89, and EQ w/o STAB won't kill Metagross with 130 base Defense, especially as if it has done Magnet Rise. Even though Magnet Rise will not be likely for a moveset, who knows?
Metagross, though Bronzong is one of the best Walls in the game, has a chance of getting rid of Bronzong.
NOTE THAT I SAID CHANCE.