An Exarch with a bright lance and no powers in a 3-man squad costs 195 pts. Two Vypers with bright lances and CTMs cost 190 pts. Both can use terrain to good effect (move-shoot-move), the Exarch hits 5 out of 6 times, the Vypers hit with 1 in 2 shots. The Exarch can only ever put out one shot against a vehicle, the Vypers can potentially hit with two. The Vypers are vehicles and so are unaffected by AP (mostly), but can be knocked down by one shot, the Shining Spears have 3 Wounds total at a 3+ save, so they're pretty survivable.
Of course, it also depends on how the rest of your army looks.
Cheers - Rax
