Space Marine Bikers or Command Squad?
Command Squad with Apothecary, 4 Storm Shields and 4 Grav Guns on Space Marine Bikes - 240pts
2x 3 Space Marine Bikers with 2 Grav Guns and Sergeant with Combi-Grav - 206pts.
What's the one to pick? In a Demi-Company, they both have Objective Secured so that's not an issue; the Bikers have slightly more firepower with the extra Combi shots, but that's a once per game deal - they also have an extra model, and can more importantly fire at two different targets/tie up two shooting units/claim two objectives etc. while the Command Squad has +1 Attack and Leadership, has possibly more consistent firepower with Storm Shields removing the need to Jink, and is overall more resilient with 3++ (I'm an Ultramarine, so 4+ Jink for the Bikers) as well as FnP overcoming the one less body.
I'm leaning towards the Command Squad so I can build the one spare bike as a Captain on Bike, who can replace Sicarius as the leader of the Demi-Company and be actually relevant rather than the awkwardness of Sicarius, but I'm not sure.