X-O Manowar by Venditti is the best Valiant book since the '12 relaunch, it hit #50 this week actually. The book has a minor slump somewhere in the middle but for the rest it's great sci-fi action.
Harbinger is really good too. It also has a similar slump in it and the ending isn't really all that (although the story is still ongoing in other books) but again, the good tends to overshadow the bad here. Also features one of the best comic book antagonists in Toyo Harada.
For pure action you got Bloodshot. Pretty much all the iterations of the book are solid to good, although I still prefer the OG run.
If you're more into comedy and off-beat science stuff, you can't go wrong with Quantum & Woody by James Asmus and Archer & Armstrong by Fred van Lente. Both runs have ended already and aren't too long, so they're easy to get into.
A book that's fairly young is Wrath Of The Eternal Warrior by Robert Venditti (same writer as X-O Manowar). It probably helps if you're a bit familiar with the character (this book is a restart after some earlier books featuring the character didn't really work out that well so there's already some history there). Either way it's a very promising start.
You could also check out some of Matt Kindt's work to see if it's to your liking. I'm not a fan of his work and generally avoid him, but he writes a lot of Valiant stuff so if you do dig him, there's a whole bunch of books you can pick up.
'Ro session 
. I'm just beginning to get a cold, so there's my out 
Madrox
at Marvel for trying to get rid of Mutants/X-Men in favor of the Inhumans.