I can't tell you which one to get, I built mine piece by piece, but I can tell you those primers on X39 ammo are not all the same. Some are deep, some shallow, unless you're using Hornady, then they'll be consistent. This is what causes the "hard primer" problems folks talk about. They aren't really any harder, just further away from the FP when it goes home.
One of two things can cure FTF with X39: A stouter hammer spring (JP yellow) or a trigger upgrade. I use Geissele triggers in all my lowers and they light off everything. It's a milled down hammer, better sear engagement, and a mostly mil-spec hammer spring. You wind up with a lighter trigger pull throwing a lighter hammer much faster, thus hitting harder. Look at the G2S trigger, it's the least expensive of their line and I assure you you will love it.
Hope that helps some, I know it wasn't in your line of question, but it'll head off problems down the road whichever upper you get.