for me, it all comes down to how you expect this thing to be used. both sizes are valid approaches, but suggest different priorities to me.
selfishly, I’m largely working with line-level gear with some mic, instrument, and euro levels mixed in. in that instance, the larger jack seems to cover the most bases.
if you’re wanting something that primarily works with eurorack levels, then doing a 3.5mm layout makes sense. if that’s the goal though, I’d also lean towards turning the thing into a full-on euro module with USB jacks brought up to the surface.
purely from an ergonomic perspective, when you have patching occurring on the face of the device, making something that prevents the heavy use of adapters is preferable to me (I feel the same way about TRS jacks and using stereo splitters). I’d rather make something bigger that has more pannable mono channels than use stereo jacks anywhere.
somewhere in lines there’s a convo around jacks where @tehn asks for input on this question and I think that directly informed norns having 1/4” jacks instead of other options (something I’m very pleased with). it might be early in the minimal mixer thread or somewhere else, but there’s good info in that chat as well.
edit - https://llllllll.co/t/1-4-vs-1-8-connections/3029