If you are looking at buying a box set, your options may be limited.
However, if you would be happy buying blisters, then a whole range would open up. Wood elves are going to be popular for a while, but dwarfs are supposed to be rereleased early next year.
Personally, I would go with the wood elves. For a unit, you can get a unit of 5 wardancers, with command, in two blisters. If you by a third blister, that would give you 8 figures, a nice size squad. The wardancers also have 3 direct sales only models which might generate more interest as these are not available in blisters.
These are the direct only ones.
Click Me
Also possible is waywatchers, although a unit of 5 or 6 here would be better.
While the scouts are fun, the box set for them comes with 16 models, so you would be able to put together 2 units of scouts, or one unit of glade guard.
The other unit that may prove popular is a unit of 3 or 4 treekin, although I don\'t know whether that is the sort of thing you want to paint.
If you want to look at the ogre box sets, then I would go for either the leadbelchers or the Iron guts. Both come in a box of four, and both can be used as Dogs of War in any army.