A GOOD PRIME LENS
Currently I own the 35 F1.8G DX, 50 F1.4G and the 85 F1.8G.
Really can't go wrong with the image quality you can get out of the lenses, but a fast zoom is also a good Idea. (I have no fast zoom anymore, except for the 70-200 F2.8, which is really a zoom) For the rest its all footwork
A 35mm is good if you want to include a jump and part of the scene. or actions of multiple dogs.
The 50mm gives you the ability to get an object as you see it. It works as a 75mm on dx but that represents the part that is in focus when you look at something. It works great for capturing moments of kids / dogs
The 85mm is a specialist lens for portraits and getting things closer. but still usable for kids /dog portraits as well
But for the rest, you can use any lens for anythink really , but a wide lens will never get close
A 85mm used to show subject and background:
A 35mm used as close-up (Image is cropped but quality remains and so allows you to "zoom" in post)
And last but not least 2 photos of a 50mm 1.4 lens: A close up and a landscape
As you can see, any of the lenses are capable of getting what you want, the 85 has the most zoom, and for work close by will make you work slower. With the 35 you can really catch anything you want, but if you can't get in close enough you maybe wanting a 50mm.
I think for me the 50mm is the most versatile for the photography that I do.. that is shoot with the lens that is on the camera Still I love them all, and use them all for everyting.