I always run [Nautilus]. I've found [Verglas] extremely helpful in virtually all situations. While I'm paying attention to the mission, a laser will regularly pop out of my sentinel and zap whatever I didn't see coming up behind me. That's that. Now for a reduced cost of "only" 5 forma!

Great for mining and fishing as well — you focus on gathering with lo-fi in the background, Verg' takes out whatever is trying to kill your vibe. Let me tell you, there is NOTHING WORSE than a MOA coming up to stomp you, or a flying tentacle demon flinging itself at you to take over your 'frame, when you have Tranq Rifle in hand and are doing your best impersonation of a prehistoric bird. This blasts them away while you line up your target — er, I mean, while you focus on the conservation effort.

Now, 5 Forma is a lot! But I run ole Naughty 100% of the time, so I invest in the best equipment for my good buddy — just as I would do for myself.
This is Warframe; robots are family and I feed him only the highest-quality raw Infested diet.

Plus, this helps out on Steel Path; [Galvanized Aptitude] is no joke. Your sentinel will prime Viral for you and the beam adds a solid 5% to your outgoing damage.

See my Naut' build here.

VARIANTS: If you're doing some serious content and want to fit in a Primed Bane of Faction mod, replace the [Speed Trigger]. It's more damage; I'm just lazy!

And for Deimos, you don't want to run Viral. Replace [Malignant Force] with [Thermite Rounds]. This will give you Blast, which isn't awesome, but it works!
Ideally you would want to run Corrosive and Heat for Deimos, but you can mod your actual kit for that...