My DC recs:
Fair warning, these are all from the original creators and might be difficult to track down in GN format.
Pre-1970s
Enemy Ace by Bob Kanigher and Joe Kubert - solid Kubert artwork as usual, Kanigher is a bit melodramatic as a writer but it works. Plot is about a WWI German airplane pilot who is believed to be an unsympathetic killing machine by both his comrades and enemy combatants. Actually, he's not. Generally episodic/one-off stories, I believe a couple recurring. The GN I have is
Showcase Presents: Enemy Ace, black + white newsprint.
Doom Patrol by Arnold Drake and Bruno Premiani - Again episodic/one-off stories, some recurring towards the end. Fun series where the female character is the heavy, and the typical manly hero faints and is pretty useless. Also there's a cool robot man and the ending is a punch in the gut. Great art and writing. It looks like you can get
Archives,
Showcase Presents or
The Silver Age versions.
Plastic Man by Jack Cole - One of the best. He did have a few ghosts towards the end of the run, but it's generally easy to tell a Cole issue from say, a Kotzky (Kotzky IIRC draws Plas like a horror monster). Very fun and inventive comic, highly recommended. There are some out of print
Archives versions.
Superman by Siegel + Shuster - I recommend the
Daily Strips, the stories are tight and its possibly the purest vision of Superman you'll ever read (a chaotic good troll). Look for 1939-1942 to start off.
1970s
Do yourself a solid and read JACK KIRBY. Anything he did at DC in the 70s is pure gold: great artwork, basically unrestricted in his storytelling, did his own writing with IMPACT. My recommendations are:
Kamandi - after the Great Disaster, sentient humans are in short supply. Sentient animals, on the other hand...
Awesome story, great characters, #29 is my favorite. There's an
Omnibus from 2018 that looks to be OOP, but it's worth it.
Fourth World - actually four titles (
New Gods,
Mister Miracle,
Forever People,
Superman's Pal Jimmy Olsen). Possibly his greatest work - the writing is mind blowing. I have the
Absolute Edition but there's other options;
Box Set and
Omnibus.
As a follow-up, Captain Victory and the Galactic Rangers. Whatever you do, do NOT read anything Fourth World that isn't written by Kirby. I've never seen a different writer understand the theme of the comic, Apokolips/New Genesis, or hell, even Darkseid.
The Demon - fairly short but otherwise fun; might be a gateway to
Prince Valiant.
Post 70s
I'm only gonna give you one rec here
Hitman by Ennis and McCrea - Ennis with oversight is Ennis at his best. McCrea can handle panels and spreads with equal impact. You know how you read a comic and some dumb corporate mandated crossover breaks up the story? Doesn't happen with
Hitman. The ending is beautiful--the writing is beautiful--the artwork is beautiful--the comic is a representation of the best in the worst of us. Read
Hitman! There's some old OoP collections but the first
Omnibus comes out in July.