I swear by scrubbing bubbles! Spray it on, wait 10-15 minutes, wipes clean. No scrubbing required. We have hard water, so the build up gets really bad in my tub if I don't clean it at least every week. Scrubbing Bubbles is the best, in my opinion!
To be honest a good degreaser works. Go to the dollar store, purchase a kitchen degreaser spray or pour and let sit. Come back in 10 minutes or so and the surface should just wipe clean. Easy one got anything harder?