The big question with the Eldar list is what weapons to mount on your various vehicles. This is a pretty complex question, and varies depending on the vehicle and your opponents, but here are some initial thoughts for the Vyper.
The common factor is that its always fired at BS3 on a Vyper.
Firstly against common infantry types:
| Kills per turn: | Imperial Guardsmen | Tau | Space Marines |
| Shuriken Cannon | 1.25 | 0.63 | 0.41 |
| Scatter Laser | 1.11 | 0.83 | 0.56 |
| Star Cannon | 0.83 | 0.83 | 0.83 |
So far, so unexpected. Shuriken Cannon is best against Imperial Guardsmen, Star Cannon is best against Space Marines and Scatter Laser is best all-rounder. Now we need to consider the costs of the weapons. Originally I looked at it as the marginal extra cost of the weapon, but for a Vyper where the weapon-load is all there is, I want to look at it as the total efficiency of the vehicle in three different configurations. I have added Spirit Stones to the vehicle as well.
| Configuration | Price | Imperial Guard | Tau | Space Marines | Average |
| Shuriken-Shuriken | 70 | 3.57 | 1.79 | 1.19 | 2.18 |
| Shuriken-Scatter | 80 | 2.95 | 1.82 | 1.22 | 2.00 |
| Shuriken-Star | 90 | 2.31 | 1.62 | 1.39 | 1.77 |
The average column here is a bit of a delusion, as it assumes that each of these three will crop up with equal chance. If we assume that Space Marines (and Necrons who have basically the same profile), crop up twice as often as Tau who crop up twice as often as Imperial Guard, then the overall efficiency changes, but not by much. Shuriken-Shuriken becomes 1.70, Shuriken-Scatter becomes 1.64 and Shuriken-Star becomes 1.59. The efficiency has decreased in each case because Space Marines are harder to kill but the relatively minor changes in Space Marine killing efficiency are still outweighed by the massive differences in Imperial Guard killing efficiency.
Conclusions
The overall conclusion is the one that I went into the exercise with as a gut-feeling – for 5 pts its hard to beat a Shuriken Cannon. The interesting thing is how similar in killing efficiency the three different payloads are against Space Marines.
I think that at the moment though, I might go for compromise and equip my Vyper with a Scatter Laser and Shuriken Cannon, if only because I have a spare Scatter Laser from a Falcon that I converted to a Wave Serpent, which allows me to use the Shuriken Cannon that came with the Vyper to upgrade the on-board Shuriken Catapults to a Shuriken Cannon. Why GW never designed their Eldar vehicle sprues to actually have the various options that are possible on the vehicle I will never know – but that’s a whole topic on its own.