Chosen chaos space marines are the Swiss-army knife of the codex. They're able to take on many battlefield roles, but they must be kitted out for such roles in advance and pointed in the right direction during the game. Much like regular troops, they have a fearlessness issue that needs to be thought about (depending on what role they're assigned), so taking a fearless character along with them is sometimes going to be a good choice. What they get over a basic trooper is an extra attack: we're paying the points for this (and for uber-grit in the old parlance: i.e. a bolter, bolt pistol and close combat weapon), so that's one aspect we should think about making use of. Being able to take 4 special weapons (5 if one includes the heavy weapon / special slot) is also very good.
So, let's have a look at a few set-ups for our Swiss Army Knife Chosen Chaos Space Marines:
9 Chosen, Mark of Khorne, Icon of Wrath, Veterans of the Long War, 4 flamers, champion with melta bombs and power weapon, Rhino Transport with Havoc Launcher (305 points)
To be run with someone like Kharn. Pile in the transport, and roll up to the enemy. The champion should be armed with one of the flamers. Get out, flame and shoot. Then subsequently charge. Use a Land Raider instead perhaps for the assault ramp. These guys should be taking down most opposition and are geared up to also face-off against hordes (which seem to be getting forgotten about, but shouldn't be since one aspect of the new meta is boots on the ground ... as well as flying).
9 Chosen, Mark of Slaanesh, Icon of Excess, champion with pair of lightning claws, 3 meltas, 2 power weapons, Veterans of the Long War, Rhino with Havoc Launcher (370 points)
An expensive option run with a Slaanesh character or Dark Apostle. Designed for tank hunting and then dispatching of the contents.
5 Chosen, Mark of Nurgle, 5 Plasma Guns, Icon of Vengeance, champion with power weapon, melta bombs (225 points)
Bringing massed plasma firepower from behind, these Nurgle boys answer the call against terminators from range and should probably hold an objective whilst they're at it. Try not to get assaulted.
5 Chosen, Mark of Tzeentch, 1 heavy bolter, 4 combi-bolters, Icon of Flame (137 points)
A Tzeentch alternative to the rear-guard action: lots of soul blazing weaponry to target infantry hostiles. Probably better ways of doing this, so think of this option for illustrative purposes only. Don't get assaulted.
5 Chosen, 5 melta guns, Rhino transport with combi-melta (185 points)
10 Chosen, 1 Missile Launcher, 2 Plasma Guns, 2 Meltas, Mark of Nurgle (275 points)
Taken in an army with an infiltrating character (as above). Infiltrate to the back lines and get at least one turn of firing in. The mark of Nurgle is there to try to get a second turn of firing in before being destroyed. This is a distraction unit to take some heat of other units in an army. Try not to be assaulted.
5 Chosen, Mark of Nurgle, 1 Missile Launcher, 2 Plasma Guns, 2 Meltas (170 points)
Just like the above, but smaller!
Overall, I want to like Chosen, but they're pricey. Overall they're okay. But the main issue is that I feel that the Elites slot that they occupy will be vying for a position with other, more appealing selections and choices.