It probably all depends as to what you want to do.
Lightroom is a cataloging and image adjustment program. It's primarily aimed at the photographer who has a fairly large collection of images and needs to correct and adjust them quickly and efficiently. Lightroom works best with RAW images, although it will handle jpeg and tiff.
Photoshop is an image manipulation program. With ACR you can do virtually everything as far as image adjustment is concerned in Lightroom, but where LR does not allow image manipulation, Photoshop does.
So basically if you have a need to store a large quantity of images, and find them again, plus make overall adjustments ( and some local ones) then Lightroom is for you. If you have a small collection of images and have a requirement to manipulate the images, then opt for Photoshop.
However whilst Lightroom is a good program it does lack some of the flexibility of Photoshop, so the majority of Lightroom users also have some additional image manipulation program, i.e. Photoshop