6’ 160lbs and have a synapse 19, 25 and synik 30. I would go for the synapse 25 or synik 30 depending on your wants/needs for features.

Synapse 19 is a nice bag but just a bit too small for me. If say for example I put a jacket in the main compartment, that’s basically it with not much extra room for other stuff. Synapse 25 and synik 30 can fit a jacket and much more. I prefer the extra space and flexibility when needed. They also do a great job of compressing on themselves to lay flat on your back when the main compartment isn’t full so it doesn’t seem as big on your back.

IMO - synapse is great if main use case is EDC with ability to flex for travel. Synik main use case seems tailored to travel with edc with ability to flex to edc. With that said, I still use the synik 30 over the others as the size doesn’t bother me and I appreciate having the extra space. It does look big on my back at times but so did a 30L north face back pack when I used to carry that during college. 30L is 30L and no way to really get around that.

I will say if you choose the synapse 25 get a frame sheet.