But the setup being described doesn't involve any sound modules, and for general ease of use and extensibility, I would say that at this point USB MIDI probably wins. If you want to go to a sound module of some sort, there are some cheap and reliable USB->DIN MIDI cables available (along with some cheap and totally unreliable ones).

USB → DIN MIDI adapters are expensive, unreliable (they may or may not work, depending on how the MIDI over USB device exactly converts MIDI in to USB), and another moving part to have in a recording studio.

It is a $50-$100 extra investment to get a quality keyboard with DIN MIDI, but those quality keyboards come with better software and have a better build quality to them.

It’s a lot better to spend the extra money up front to get a keyboard with a DIN MIDI connection (e.g. an Arturia Keylab or Novation Launchkey) than to have something which will need a hacked together USB-to-DIN box (and I notice I haven’t seen any names of make and models of MIDI USB to DIN boxes which supposedly will always work) if they ever want to go DAWless.

I have a bunch of older stuff that only has 5 pin MIDI. The adapter I use is made by Yamaha, it hasn't let me down even once over a year and a half of pretty heavy use.

Retrokits rk006 is amazing for this (usb host mode) -> DIN midi all ways bridging.

USB to Midi cables usually still need a computer or a synth with USB host functionality. You can not connect a USB Midi controller to a 5 pin din midi synth.

Some synths offer a USB Midi host functionality like the 1010music Blackbox, the Deluge and most of the Raspberry Pi based synths like the Monome Norns.