Can someone please help me buy the right version of rebellion?

I already have sins, diplomacy and entrenchment and now would like Rebellion. I can see Rebellion and also Rebellion New Frontiers.

Both have exactly the same descriptions on places like Amazon and I can find each at quite varied prices with rebellion sometimes more expensive than new frontiers and vis versa

So do I buy both or do I only need to buy just the New Frontiers version and not waste money buying the basic Rebellion version please?

Thanks in advance