Verified answer

Use the m1 garand (or m14 if you don't have the m1) because those guns get good range. Then use at mines because the rpgs don't do very much damage to tanks (the at mine is a 1 hit kill on everything but the heavy tank, which takes 2). Then use the ammo upgrade so that you don't run out of rifle bullets (m1 and m14 run out fast). Also use explosive upgrade so that you can do more damage to gold crates (or whatever the box things are called). Just sneak in and throw all you mines on top of the crate, then throw a frag on it, and boom 400 points.

It all depends on your play style. For vehicle killing you'll want the RPG, as it can lock on to the tracer dart. I have a friend who uses the shotgun as an engineer, as it's a one-hit kill point blank. However, until you get slugs it's a little difficult to use from range.

Just use whatever your best with. If you want to kill vehicles though, make sure you have the tracer dart. Both the RPG and the Carl Gustav will lock onto them. The AT4 does the most damage vs. armor, but it's lazer guided.

There is no own-them-all load out, it all depends on your preferred style of play. I prefer RPG-7 (on vehicle maps otherwise Carl Gustav), Revolver and the best available SMG - when grouped with friends or competent others I may switch to the Tracer Dart, esp. if there are helicopters on the map. Some of my friends however prefer SPAS + Slugs.

As far as traits go I go with increased laucher ammo and increased explosive damage - vehicle traits are entirely up to you, I switch between extra armor, smoke screen (if there are many engys on the map) and fast reload.

If you want cheap, quick kills, then go with the Saigia, it only holds around 4 shots per clip, but it is a SHOTGUN WITH A CLIP SO IT RELOADS FASTER!!!!!!!!!!! it is awesome.