However...the thought occurred to me...which team do I use?!
For my first team, I went with a squad of 5 Plague Marines, two armed with melta guns, whilst the champion just has melta bombs. The Plague Marines are toughness 5, with feel know pain and carry blight grenades, negating a single extra attack from one opponent when charged, very useful. Next I choose a 10 man cultist sqaud, with one being armed with a shotgun and another armed with a heavy stubbier. The advantage here is numbers and toughness, having agonised as to whether or not to upgrade the cultists with Toughness 4 their save is terrible, but toughness 4 makes them as resilient as a normal Chaos Marine.The toughness and resilience of the Plague Marines has come into their own in countless battles. That all important +5 Feel No Pain is invaluable, plus being Toughness 5, Fearless and wounding on a +4 with their plague knives is a very nice package!
The cultist however are a little more...squishy. If I use them right they can hold objectives, with careful placement the leader can give them back up. The heavy stubber can bang out three strength 4 AP5 shots, whilst the two melta guns can take heavily armoured foes, monsters and tanks, whilst 5 cultists are armed with autoguns, giving some more ranged options.
Next I choose a second Kill Team, this time using a 5 man squad of Thousand Sons, backed up with a Rhino with havoc launcher. Whilst only numbering 6 models, the idea would be that the Rhino can zip around the board, depositing Rubricae at the objective, relying on their power armour and invulnerable saves, whilst dishing out AP 3 bolter rounds.
The added bonus of this force is the Aspiring sorcerer, and is one of the few forces to utilize psykers, making them deadly in Kill Teams games. The downside to this force is the numbers, however to be able to field a squad of powerful miniatures led by a sorcerer in a tank is too good an opportunity to miss!
The other team I could take, is to simply swap out the rhino for 10 cultists, with no further upgrades. This gives me the numbers whilst still retaining the elite Rubricae cadre, giving me more flexibility on the battlefield. The cultists are just armed with a pistol and close combat weapon, but can still knock out 3 attacks on the charge, and can spread out to cover the Thousand Sons. keeping the Sorcerer close to the cultists means that they can use his leadership should things get tough, also providing him with a suitable meet shield should he need it!
A variation on the Plague Marine team is to swap out the cultists for a Spawn, which has 3 wounds, variable attacks and mutations rolled before engaging in a fight. Couple this with the Mark of Nurgle and you have a effective individual!
Although it has no saving throw, they hope would be to draw fire away from the five Plague Marines. The champion is now armed with a power weapon, whilst the two meltas are still included. This time, the Weapon Specialist will be one of the meltas, increasing his range by half, giving me a 18" melta weapon! Eternal warrior will be given to the champion, meaning that whilst he still has the one wound, it will mean that he will get his +5 Feel Know Pain save against a shot he normally wouldn't be allowed to save against.
I have a few more options I would like to try out, Raptors, Warp Talons, Possessed and even the basic Chaos Space Marine are all viable choices.
Death to the False Emperor!