BFG: Chaos Navy

The typical Chaos cruiser is armed with longer ranged weapon battery and lance broadsides, medium armor (5+), and moderate speed (faster than Imperial and Tau but slower than Eldar and Necron). As such, the Chaos fleet is frequently successful by using their speed to attack from longer ranges. However, no fleets would allow itself to be shot from long range without trying to close range. Thus the Chaos fleet will need to counter this by either keep moving to maintain range or close and pass through. Keep moving typically will only work for so long given the limited table top playing surface. Closing and passing through nullify for a period their advantage in weapon range. There is a third option, and that is to close and pin the enemy with a portion of your fleet, while the majority stand from afar unmolested and shoot. Ships choices should keep the above in consideration.

The Cruisers:
The Slaughters = good. The slaughters have only short ranged weapons but compensate for this by having a faster approach and more powerful broadside than most Chaos cruisers. Given these atypical traits that set it apart from most Chaos cruisers, it should be used apart from the main Chaos fleet. Thus it might be used as bait for the enemy to chase, but few competent opponents would fall for this. The best use for the slaughter would be to close with the enemy fleet to force a firefight and thus pin the enemy. This is in essence an active bait role. If taken for this function, two (or three?) slaughters work better than a single ship. A single slaughters would be better as a counter attack or reserve cruiser.
The Devastation = good. Without torpedoes (the Chaos fleet is short on torpedoes overall) however, their attack crafts are less effective. Thus the attack crafts of devastations to be more defensive in practice, with only occasional opportunities to feign and or actually make an attack run. This is why the devastation is rated good rather than excellent. But given long ranged lances the devastation can still contribute to the fleet attack (its batteries are defensive).
The Carnage = excellent. The carnage can deliver 10 battery points at 60 cm and 16 at 45 cm, or 2,3, 6 attacks against capital ships abeam at 60 cm, 45 cm, 30 cm. These guns provide extended coverage against Eldar from afar and give the carnage the option to close for broadsides. This flexibility to attack from afar or up close make this an excellent ship.
The Murder = poor. Compared to the carnage, the murder has shorter range batteries and less firepower. While it is armed with 2 lances, the lances cannot combine with the weapon battery broadsides. The lances are forward firing yet the chaos fleet is best encircling the enemy at range.

The Heavy Cruisers:
The Acheron = average. This is a lance ship but at 60 cm no better than the devastation and at 45 cm adds only two more lances.
The Hades = average. The hades is in essence a murder with an extra two lance that can be added to its broadsides. If you are looking for a long ranged ship with both batteries and lances, then this might be considered, but two hades is probably not as effective as a devastation and a carnage.
The Styx = average. This is another carrier like the devastation. It costs 50% more, has 50% more attack craft capacity, but same number of lances. The devastation is a better buy.
The Repulsive = above average. Medium ranged batteries and short range lances seems an odd combination. It should be upgraded to have medium ranged lances instead. Having 10 hits rather than 8 means that you can take this ship into the heart of the enemy fleet and duke it out. It costs about 50% more than a slaughter and is armed 50% more as well, and while the slaughter is faster, the repulsive with medium rather than short range make the ship point effective. One thing good about it is the torpedoes it can add to the Chaos fleet.

The Battleships:
The Desolator = good. This is another lance ship but is actually reasonably armed. At 50% more than the devastation it actually has 100% more long ranged lances. True it is not a carrier but with a salvo of 9 torpedoes, it sufficiently compensates.
The Despoiler = above average. This ship firepower wise is about as effective as two devastations. But two devastations has 16 hits instead of the despoiler 12. But given that it can be upgraded to have torpedoes, the despoiler becomes the only combined torpedoes-attack craft carrier in the chaos fleet. That is why the despoiler is above average rather than poor.
The Planet Killer = above average. At 505 points it is very expensive, but also well armed with 18 points of broadsides and 6 lances at 60 cm. Then there is the armageddon gun that can be very devastating but requires reloading (which will also reload the 9 points of torpedoes) and it can misfire. I agree that it should be a unique occurrence to field.

The Escorts.
The Idolators = good. This escort has 45 cm batteries that do not suffer a column shift above 30 cm, along with 2 turrets make this a very capable escort. Add in the lance and this escort in a squadron very able to take on capital ships point for point.
The Infidel = average. Sure it adds torpedoes to the Chaos fleet, but to fire it as one salvo the ships have to be in base to base, which make it vulnerable to having one hit take down the shields on each of two ships in base to base. In general I am not a fan of torpedoes on escorts.
The Iconoclast = average. Poorly armored but reasonably armed, and cheap. You get what you pay for.

In summary the mainstay of a chaos fleet should be devastations and carnages. It should also contain a detachment of slaughters or a repulsive. Sprinkle in a squadron or two of idolators. Lead it with a desolator.