Which rail? 0 MOA or 20 MOA?

I just need to order one and not sure which one. What is the difference? And which one is a better choice for a centerfire rifle?

For 99.99% of people, a zero moa rail is what you need. Unless you intend to regularly shoot at 800+ yards, you don't need a 20 moa rail

What scope is going on said rail?

Either a Swarovski X5 or Nightforce ATACR

If you plan to dial elevation, going with a 20 MOA pic rail gives you more elevation travel. Many scopes, including the NF, are designed to be mounted on a 20 MOA cant. I don't know about the Swaro.

You will like that atacr

What reticle do you like on the ATACR?

What rifle/caliber is the rail going on?

One is a 338 Lapua and other is s 6.5 Creedmoor

I believe it's the mil r. It's pretty straight forward

Sounds like you are in the .01% I mentioned. Haha

20 MOA rail on the 6.5 Creedmoor, 30 MOA or 40 MOA on the .338 LM. Because it is a waste of ammo to shoot the 338 inside 800 yards. Unless you are cutting hogs in half with it, then ammo price is no longer a factor.