I personally really favor the current ASUS stuff. It's super easy to flash unlocked software which gets you access to everything, and out of the box they have a bunch of built in goodness like USB printer sharing (without requiring proprietary software), file sharing, DDNS, bandwidth limiting per device and a bunch of other stuff I use all the time.
They also have a really good app that lets you do just about anything remotely.
As far as file transfer, I can easily achieve 80-100 MB/s over wireless from a local share, which is only limited to a max 128 MB/s by the 1 gbps Ethernet. My family and I use Plex all the time off said share and can confirm they work well with a NAS.
I have a bit of an older model, but the AC88U checks off all those boxes and is good bang for buck.
As an example of the convenience of an open router and what you can do, you can check out my post I made about a year ago about router level ad block. https://forum.level1techs.com/t/diy-router-level-ad-blocking-anyone-else-doing-this/85396