C5400 is actually my daily driver for a long time now.

C5400 is literally the C3150 with an extra 5Ghz band, they are very similar device but with beefier specs.

It comes with 8 antennas. To be frank, the signal output is rather similar with C3150, what it excels is the performance when you have many devices connected.

Tough choice for me.

I would be more towards the C5400 as it has a better wireless coverage. I value wireless coverage over those features.

RT-AC86U still a great device coupled with AiMesh you can add another node to your network in the future. Not to mention AsusWRT is really feature rich.