After I saw this I thought it would be fun to do so I had a look at what armies I would like to paint 1000 points of and came up with 6 armies.
1. Chaos Space Marines - I have a demon army already so these would sit nicely as allies it would be all plague marines and Nurgle themed because I love Nurgle.
2. Dark Angels - I have always liked the Dark Angels but the fluff is not as good as it was so I would make a Deathwing force based off the old native American theme.
3. Grey Knights - I already have a batch of Grey Knights so this was the one that makes most sense as I have unpainted models but when has that ever stopped us hobby addicts.
4. Militarum Tempestus - Guard are awesome but I will never paint a full force of guard platoons in 30 days so I would focus on the veteran guard with armour to support.
5. Necrons - I have a sizeable Necron force already painted so the force would expand that army which is the only reason Necrons are on the list.
6. Tyranids - possibly the most expensive force on the list as its a hive tyrant, hive guard and Tyranid warriors and will be a shooty army.
Ideally I would like to play someone when I am done so if anyone has thoughts about the army choice or would like to participate and play me at the end of the period that would be cool.
I will make a decision in regard to the force in the next few days and I will post the result here