The battle force box is a decent deal, as is the windrider host box if you can find it. Depends if you want to run jetbike or guardian troops. Jetbikes are probably better in a cad, but guardians are much improved in a warhost, tho you'll need three groups of them.

For thousand points, I would suggest the battle force box and a farseer. That gives you two troops and an HQ, and the box comes in around 500 points once you figure in upgrades. From there, you can add 3 aspect warrior squads, which will be another 400 points, then give them an aegis. It will give you a lot of variety for painting, and you can add in squads later to make a warhost.

Really, all the aspect infantry have a use now, just depends on what you think would be fun. And I am assuming that is your aim, rather than a spammy tournament list. There are just so many directions you can take it if you are aiming for something casual and fun.