Everyone raves about Dubai Frame for skyline views but it's 50 AED for basically a photo op. Architecture student in me appreciates the frame concept but Zabeel Park is free entry and you get nearly identical panorama of old Dubai vs new Dubai.

Park has elevated areas near the lake where you see both Burj Khalifa and Creek area perfectly. Plus you can actually sit down, have a picnic, take your time instead of being rushed through crowded observation deck.