Both are great looking cases and would match well with the Natural Titanium, but I think it comes down to preference of material that both cases use. The Apple silicone is quite a bit lighter, but it is just that, Silicone. Whether or not you can live with that, that's up to you. It attracts quite a bit of lint, and can be a bit cumbersome to pull out of your shorts/pants pocket. The sheath, is a slightly heavier case, but does not add too much bulk IMO. If you've never used a Sheath before, the texture is more of an "eggshell" type of texture, which in my opinion is very comfortable to hold and provides great grip. It fits the phone perfectly. If you have ever used a oneplus phone, the grip is very similar to their Sandstone case. Also, it would provide much better protection than the silicone, and would fair a lot better in the long run.
Sorry for the novel, if you want my recommendation, I would say the Caudabe Sheath, or maybe even the Caudabe Synthesis since they just released that case in the Gray color. (I own Sheath, Synthesis, Silicone all in Gray).