I've been using Sketchbook Express since it came with my tablet, and it's a relatively simple program and really good all at once. I've wanted to go back to SAI but I'm not sure if I'd still be as comfy D:
Well to be honest I didn't want to stop using Artweaver, my first art program either so I kinda just slowly went on to Sai, then went back to artweaver until I finally stuck with Sai.
Oh, alrighty. I don't think it's free since it came on a disk with my tablet so I don't suggest it lol. I've tried gimp before; was it really laggy for you, too?