Which Suit Upgrades First

[Cystem]

So this is my second playthrough but on Nightmare. I was thinking about getting "Frozen Enemies Drop Health" first - wadd'ya think?

[UNBREAKABLE]

I usually save up points until the midpoint of cultist base - then buy faster dash refill, faster switch speed and faster mantling. Those are critical to surviving and also dishing out damage. Then move onto double frag grenade, then ice bomb. Maybe the ammo barrel upgrade too if I have the spare points.

There is no best order really, I just like mobility and utility so I upgrade those mechanics first. I think the exploration perks are blatantly useless though outside of a blind run, always save them for last if you can find secrets just fine.

[Get Out]

Go for double grenades. It's such a massive improvement. You can literally delete heavies from your screen just by pressing CTRL twice and shoot them with whatever you have.

[Sar]

Faster Dasher IMO, but on UNM I always went for the one that removes barrel damage first.

[Steel]

The one that lets you swap weapons faster, then the two ones that lets you dash more often (less cooldown and refresh cooldown on glory kills), then all the ice bomb stuff.
That's my priority, after that it kinda doesn't matter imo as long as you avoid the bad collectible hunting ones.

[D.T.]

All fundamentals, starting with dash. Dash upgrade is a game changer.