AC3100 or AC2900 as the Primary Router

Hi Guys,

I currently have a AC3100 router and has recently been able to get my hands on a AC2900. I want to setup a AiMesh network. The routers will be connected via ethernet cable. Which one should I setup as the primary router? The primary router will be in the basement so probably the AC2900 should be the primary? It also seems to have a better processor. Am I correct?

Thanks!