GD Library vs ImageMagick

I need to implement the following: a) Get the image height and width of images b) Create thumbnails and other lower resolution images from one high res image The site is expected to handle a large number of such operations with bulk uploaded images. Which would be better for implementation - gd library or imagemagick? For the latter, I read that some additional overhead may slow down operations as php will need a pear module to call imagemagick functions. Any help or link to a relevant article is welcome. Thanks for the trouble, Arijit