Noob in nees of guidance.

[Wataterp]

What does the Helios and Carrier do? What are their differences and similarities? Which one should I get first?

[Shoryuu]

Helios and Carrier are sentinels, they act like Kubrows and Kavats. They have abilities like vacuum, which picks up drops for you etc. 

Helios can also scan objects provided you have scanners equipped or that widget from Simaris that gives you infinite scanners. 

I prefer carrier personally, but it's your choice which you pick 

[Omega-Shadowblade]

To add onto Shoryuus info, Carrier also acts as an ammo mutator; picking up ammo that doesn't match your weapon and changing it into ammo that does match (at a lower amount).

[(PSN)KyleXY12345]

Helios is a sentinel that scans stuff for you and is useful if you want to complete the codex. It has deconstructor as its weapon and its actually a pretty damaging sentinel weapon.

Carrier on the other hand is all about ammo economy. Carrier makes your ammo problems go away with his ammo case and is also really useful for vacuum since he breaks containers with looter.

[(XBOX)calvina]

The Helios is a sentinel that has the ability to scan enemies for your codex, which you find on your ship, the opposite side of the maetplace console. It also has a weapon names the Deconstructor, which in it's simplest form, is just taking pieces of itself and throwing parts it at the enemy.

The Carrier on the other hand, has the ability to pick up ammo that doesn't match your weapon type and turns it into usable ammo. (For example, you have a rifle, you walk over bow ammo, the bow ammo is turned into rifle ammo, at half the amount.) Another plus is it also increases your maximum ammo capacity. For its main weapon, the carrier uses a shotgun called the Sweeper.

Edited July 20, 2018 by (XB1)calvina

[RobWasHere]

Get carrier first because its easier to get. Helios require research in dojo and 2 forma to build, unless you go straight for prime version.

As people said before me - Carrier makes your life easier with Ammo Case that automatically transmutes picked up ammo to ammo you need. Simaris has additional mod for it, Looter, that automaticaly tries to break all containers in small radius around you in case you miss some.
Helios is more specialised sentinel. Using scanner charges it scans enemies and objects to fill up your codex. Codex shows spawn locations, weaknesses and loot tables for easier mod search later. Enemy that has codex entry completely filled can be spawned in Simulacrum. Simaris has also additional mod for it, Detect Vunerability, that makes Helios place weakspot on enemy that has codex entry filled. Shooting at weakspot gives 2x damage bonus. Helios also has unique weapon, installable only on it, Deconstructor. Its fairly strong, counts as thrown melee weapon and has special trait of always aiming at heads. Carrier's Sweeper can be installed on other sentinels.

[Veridian]

Helios Prime is easier to get than the normal one, honestly.

If you feel like scanning things go with Helios, try to get the solar widget as well, so you'll scan everything for free. You will even get rep with Simaris with the widget.

If your weapon is not ammo efficient go for Carrier, everyone seem to praise carrier and I see why, but if your weapon never runs out of ammo his most valuable trait is void.

Or if you don't want to bother with any of them, the starting one (taxon?) is a decent option as well.