Compound, you are not alone in your love of Ninjak. His was the first series I tried as it was just starting as I was getting back into comics and was blown away. "What if James Bond was a Ninja?" Was how it was pitched to me.
Eternal Warrior is my absolute favorite - his storyline is all over the place but it actually works. You get some sword & sorcery, some post-apocalypse, some sci-fi - really good and really diverse. Plus you get to see talent like Greg Pak and Cary Nord pop up.
I have their whole line in my pullbox, so some of my favs:
X-O Manowar (...of course)
Archer and Armstrong
The original relaunch of Harbinger, up through Harbinger Wars.
Bloodshot
Divinity
Imperium (though it helps to read Harbinger first)