The Bike squad can be thought of very similarly to a mobile Tactical squad. It carries decent anti-infantry firepower with twin-linked bolters, can take two special weapons at any size, and can take either a heavy bolter or multi-melta on an Attack Bike. Like the Tactical squad, it prefers to stay at medium to short range and shoot at the enemy, and it will do just as little damage in close combat. Unlike the Tactical squad, it is very fast for a Marine unit and more durable with T5. Cementing the comparison, Bike squads become Troops if you take a Chapter Master or Captain on a bike as long as there are at least 5 models in the squad.
There really isn’t much argument; Bike squads are great Troops choices. They can bring lots of firepower to bear on any target with their mobility, and they are durable enough to take a beating and keep fighting. They can use Combat Squads to saturate the enemy with targets, just like Tactical squads. As an Objective Secured unit, they’ve got the speed to steal objectives from the enemy. Even without being Troops, Bikes are a very useful unit for their mobility and durability.
The most common load-outs I see carry two meltas for anti-armor or two grav-guns for dealing with heavy infantry (the grav-gun becomes much better on bikes because they are Relentless). In either case, an Attack Bike with multi-melta adds another very strong shot. Heavy bolters are rarely taken because the squad already kills infantry pretty well, but they’re not a bad choice if you are looking for more anti-infantry shots.
When using Bikes, try and keep them out of assault range of the enemy. If caught in assault, they are easily tied up and their firepower neutralized. The grav-gun configuration works best here due to its longer range, but the meltagun version can be kept safe with careful placement to reach vehicle targets without getting close to infantry.
I would be remiss if I didn’t mention how much White Scars Chapter Tactics do for Bike squads (this also applies to Attack Bike and Scout Bike squads). They always pass Dangerous terrain tests and get improved Jink saves and Hammer of Wrath hits. They also get Hit and Run, which means that you really don’t have to worry about the enemy assaulting them. The bikes can always break away and maintain their fire. If you’re planning on running a lot of bikes, these Chapter Tactics are amazing. I also see some players running Iron Hands bike armies for the added durability, but I really think they are missing out on the amazingness that is Hit and Run bikes. A more durable unit can still be locked in combat and, while it won’t die easily, it also won’t be killing much or securing any objectives.
Attack Bikes are to Devastator squads what Bike Squads are to Tactical squads. They are fast and durable, but they all carry a heavy bolter or a multi-melta. You can take up to three Attack Bikes in a squad. While you can take a squad with all heavy bolters for more anti-infantry firepower (an amusing idea with Imperial Fist Chapter Tactics), the most common configuration is to load the squad out with multi-meltas. These short ranged but devastating weapons benefit greatly from the mobility that the bikes provide.
Beyond that, there is not much to say. Drive the Attack Bikes toward important vehicles, try to not get them assaulted (they are pretty survival to shooting with 2 T5 wounds each), and then blow up the vehicle. If you are taking Salamanders Chapter Tactics, Vulkan He’stan makes this squad even more dangerous by twin-linking the multi-meltas.
Scout Bikes are a few points cheaper than standard Bikes, and sacrifice a point of WS, BS, and Armor Save in exchange for Infiltrate and Scouts. The squad can’t take any special weapons other than a combi-weapon on the Sergeant, limiting their flexibility. They can take cluster mines, which allow you to make a single piece of battlefield terrain count as dangerous terrain for enemy models. This can be handy in order to deny an important piece of terrain to your opponent. Keep in mind that dangerous terrain will not affect stationary models, so it won't do much to static shooting units in ruins. Try to mine a piece of terrain that your opponent will have to advance through, probably around mid-field. Up to 3 Scout Bikers can switch out their twin-linked bolters for astartes grenade launchers, which allow you to rapid fire frag or krak grenades out to a 24” range. While not as good as special weapons, these are cheap and give the squad respectable firepower against light infantry and low armor. With their speed, Infiltrate, and Scout, Scout Bikers should have no trouble reaching vulnerable infantry holding objectives or vehicle rear armor.
Scout Bikes are a very niche unit. They have a ton of deployment options but are relatively easy to kill for a Marine unit and don’t carry that much firepower. I would run a mid-size squad of them with a combi-melta on the Sergeant, and would outflank them in most circumstances. Since they do most of their damage with shooting, they should be able to enter from a flank and blast an enemy unit within 36” (anything within 24” of the table edge can be rapid fired).