Personally, I found the survival levels to be extremely challenging. How someone managed a 4 hour high score is beyond me. Anyway, because it is mostly charging enemies that spawn, relatively few weapons are effective across the board. However, the chain gun seems to work well no matter what the enemy. So, you just have to avoid running out of ammunition and accidentally blowing yourself up with a grenade or rocket. This means that you need a level with health and ammo pickups. Additionally, levels that allow for strafing in an uninterrupted circle are best. Essentially, the best level for I have used attempting a bronze time is Deep Hole. A horde of kleer skeletons will be the first to spawn. If you strafe along the sides of the canyon, most of them will be unable to attack you, running into a wall instead. Just avoid the bolas. After approximately the 30 seconds, sirian werebulls run down the hill so they must be considered a priority. At around the 1 minute mark, beheaded kamikazes will arrive and just like the werebull must be given priority. Additionally, bio-mechanoid majors will appear at the top of the hill and fire rockets. Though, as long as you can avoid these, they offer no threat.
To summarize, choose Deep Hole. Equip the chain gun and strafe backward around the edges of the hill. Watch out for werebulls, kamikazes, and missiles. Keep an eye on health and ammo and run to the center for pick ups if needed. You only have to survive 1:30 for the bronze.