This is kind of my take* on the map, using Okeano's format:
*Note: I've mainly played west side spawn, so I'm not as familiar with east spawn locations.
I've found up in B3, you've got good shots towards things in the A5-6 region, as well as across the field, some spots into the town, and things at D5. You can also push down the A line, reinforce the town, pull out and go south, etc. I've also had some success working the hills at H5-J5 to try holding back people pushing from the south bridge. The ridgeline at J3-K3, I've found that people will gravitate to it normally, so there's usually people already there (and you're not always spotting targets yourself).
B8-9 from the B spawn I've found to normally have campers, but not actually have a very good position for firing on a wealth of targets. Instead, I normally would go down the A line or D7 corner or go south. G7 allows you to fire on most things in the center, things in the west side's spawn, and if you're careful you can go around the mountain at G5-H5 (depending on circumstances). (Note: from the west spawn & in a light, I've taken a position above G7 and used that to spot the swamp and east spawn/bridge) Pushing the K line from the east spawn also gives some cover & if you've got decent depression, you can pop out at various locations to shoot at things in the south town or the H5-J5 hills. I've always found D9-E0 to be way to campy for me. Much like the B8-9 spot, you're really passive and don't actually have good shots on things until the battle is half decided. Furthermore, there's normally going to be someone who parks behind some bushes there (or artillery).
Needless to say, I tend to avoid the center of the swamp like the plague.