The whole line of Valiant titles are incredible and definitely worth checking out. One of the best companies out there today.
I'd probably suggest starting with X-O Manowar. The first run of the book is easily available in hardcover as well as the first volume of the new series, and it's a great gateway book into the world of Valiant. You get that super-feeling but done in a very Valiant style.
Otherwise I'd say give at least all of the current titles a chance. Shadowman has a cool mystical element to it, Archer and Armstrong has the buddy team element, Bloodshot and Harbinger are brutal and intense and the upcoming Quantum and Woody brings a lighthearted comedic element. All bring something unique to the table and are really up to the reader as to which ones are worth picking up. I currently read all of them and love each of them on their own merits, hopefully you'll give the company a chance.
Like I said though, I'd start with Manowar.
Hope that helps
EDIT: I'd also be willing to answer any questions you might have.