So as far as weapons go, it seems like you need a good maxed out sniper, and a good elemental fusion rifle (is void best, or does it change depending on the mission?). What else? Machine guns or rocket launchers (or both)? Are auto rifles useful? What about scout rifles? I assume shotguns are worthless. Hand cannons?
I'm trying to get an idea about what to acquire and level up.
Rangers had some good advice. Just wanted to add my own $0.02.
The first set of weapons you level depends almost entirely on your play style - and a bit on your luck.
For play style, do you take the minimum number of shots possible (everything is a headshot) or do you spray bullets?
If you spray bullets:
Primary - use an Auto Rifle. This will give you maximum ammo capacity and a fairly decent hit rate. Pulse rifles are supposed to be slightly more accurate Auto Rifles, but currently they are very under powered.
Secondary - I would choose a sniper. You will do most of your damage with your primary, so you won't be pulling this out much - but when you do you want it to hit hard. Note that if you find yourself needing heavy hits up close you may want to swap this with a fusion rifle. But an auto rifle can drop most targets up close to mid range really well. So this gives you a long range option.
If you play for accuracy:
Primary - once you can use one, it is really hard to beat a good hand gun. They hit hard, and crits can one shot most mobs in the game. There are also good ones that you don't need to rely on drops for. The Devil You Know can be purchased for Vanguard Marks. I have Hawkmoon, The Last Word, and Thorn - and I still use my The Devil You Know most of the time when I am running with a handgun.
That being said, the auto-aim on a hand gun really gets some people. Scout Rifles are a good alternative. Since the buff, they are almost as effective as a handgun - and more effective at mid to long range.
Seconary - I would run a fusion rifle. These have relatively large clips, can kill most things in one shot, and carry a good amount of ammo. Sniper is not ideal, because you can use your primary almost like you would use a sniper. Shotguns are up close weapons and practically worthless in PVE.
For your heavy weapon - start with a machine gun. My reasoning is quite simple - for the strats most people use for VoG and Nightfalls, rocket launchers are extremely difficult to use. For instance, the most common VoG Atheon strat is to have everyone hide inside the relic bubble and shoot Atheon. You will kill yourself if you try this with a rocket launcher. I've seen more people die to their own rockets trying to imitate the "Take Atheon down in 17 seconds with 6 Gjallahorns" video than to Atheon himself. Machine guns are also great for dropping shields and then switching to something else. So you tend to get more bang for your buck with heavy ammo packs.
That is general advice though. A lot of this depends on what you have access too. For example, Thunderlord is overpowered as a machine gun - so I like using my exotic slot on it if I can. Other machine guns (For instance The Swarm) are nice but seem to run out of ammo too quickly for my liking. If you happen to have a Gjallahorn, that is heads and shoulders better than any other heavy (except Thunderlord
). If you happen to get one of the better exotic primaries (The Last Work, Hawkmoon, or even Suros) then you may consider running with it instead. I know many people who won't unequip Ice Breaker because of ammo regen.
I think most people build weapon sets around their exotic. The important thing is to balance your set. Have at least one weapon that is good at mid-long range. Have one that is good at close range. The other pick to balance the strengths of your other two.
For the record, I typically run 3 sets of weapons:
General Purpose - handgun (The Devil You Know), fusion rifle (Light/Beware), machine gun (Thunderlord)
Good balanced set. Gives me solar and arc damage - and I can always swap in Atheon's Epilogue if I need void. I use this for pretty much every encounter except Atheon in VoG. (for Atheon, I use Atheon's Epilogue, Ice Breaker, and Thunderlord - but that is a special case based on what I end up doing the most). This was the set I leveled up with. I did my first raids with it and it worked great. Now that I have more weapons, I specialize more, but this is a great set.
Precision Set - Scout Rifle (A.1F19X-Ryl), Sniper (Ice Breaker or Patience and Time), Machine Gun (Thunderlord).
Really good at long distances. Thunderlord is insurance in case things get close. You could call this my "solo the nightfall" set. It takes forever, but I never need to get close enough to anything to let it shoot me.
Crowd Control - auto rifle (Aetheon's epilogue / Suros Regime), fusion rifle (Light/Beware or Pocket Infinity), Rocket Launcher (Admonisher III)
This set sprays bullets. I honestly don't get many precision kills with this set - but I can eat through an angry pack of hive or fallen in seconds. Really ammo intensive though. I always make sure I have a half dozen of each type of ammo pack if I'm running this setup.
For elemental damage, Rangers is correct. Doesn't matter in most places. I would recommend never leaving home without solar - because hive wizards are the worst mob in the game. But other than that, having a variety of types available is good - but don't stress it if you end up with all solar for your first set.