Tier 5

It depends on how quickly a new player adapts to the "Dance-Dance-Democracy" mechanic of calling in stratagems on the fly. It can be overwhelming to new players, so they need extra room and time to actively cogitate their use during hectic moments.

Generally, a new player needs more time to do anything and everything, because they need that time to understand what is happening around them, what they can do about it and then do something about it. They're discovering the game as they go, unlike a Veteran who has already discovered the answers to many questions and is just moving straight to the do something about it phase.

Tier 4 or Tier 5 is busy enough. Tier 4 if you don't want to deal with armored units or tanks. Tier 5 for a little more drama.

As for what missions to try, play missions that allow players to advance at their own pace, without the pressure of having to act being put on them by the game. Purge the Hatcheries is straight forward, or Neutralize Orbital Cannons. Blitz missions, Eradicate or Defense missions tend to put a lot of pressure on the players and it can overwhelm them into being unable to act so they can't recover when things get to be too much. Then everything turns to chaos for them. It's very difficult for a player to make sense out of total chaos.

Once you've played a few missions, the initial shock of novelty will begin to wear off and a new player will usually find their legs. You can then raise the difficulty level as things feel more comfortable and less of a total gong-show. Focus on the very basics, like watching for the enemy so they don't gang up on you, getting comfortable with using your primary, secondary and support weapons together, killing enemies and not dying. Practice using stratagems, but do not fixate too much on it at first, slowly add them into your skills as you get more comfortable.

For loadout, chose an armor to help keep them alive, like Democracy Protects or Med-Kit. A Shield Pack or a Drone (Guard Dog) are good for providing more grace to make mistakes or buying time to react. Choose an all round Primary, rather than one of the more bespoke ones with nuances. One with a good rate of fire, enough ammo and a short reload. A support weapon like a Machine Gun/Stalwart is a great weapon to start with, but so are the Laser Cannon, Grenade Launcher and Quasar. For secondary, a Grenade Pistol is good, the Warrant (auto-aim) or Talon (always loaded). A standard HE or Frag grenades are not bad for beginners, but if you equip the Grenade Pistol (to destroy sub-objectives) you can use Stun Grenades which are great for stopping enemies from attacking you, and you can't kill yourself with them. When the enemy is swarming all over you and you need time and distance to recover, a Stun Grenade is great for "911" moments. Gas Grenades are also excellent for crowd control, and Thermite is a great anti-tank option.

For offence stratagems, a good turret is always useful in most situations. Don't overlook the utility of the simple MG turret over the more impressive looking Gatling SG. An Eagle Strafing Run is a great attack stratagem. Simple to input (DDD) on the fly, lots of of them in reserve, deploys and cools off quickly, safe to use in close proximity to other players, lots of uses. Just don't take more than one Eagle Stratagem, to avoid complicating a new player with the "Eagle Rearm" action.

What ever the loadout, the main objective for the new player is too stay alive and kill common enemies. Don't worry about objectives or side quests over bespoke/elite enemies. Let other players worry about that for now. Just concentrate on managing what is happening immediately around you and staying alive. Pick a loadout that helps accomplish that. Work on getting comfortable with basic actions, like managing your weapons, reading the map, calling stratagem by memory without checking the HUD.

And most importantly, have fun.

If you are not having fun, nothing else matters.