donington is a great choice because it's simultaneously massive (in terms of spectator banking), compact (in terms of distance you need to walk to get to said banking) and gives you a great view of as much of the circuit as possible whilst still enabling you to get pretty close to the cars.
anywhere along the craner curves is a great choice - there's plenty of space to settle down and get comfortable without being crowded. walking right down to the bottom will give you a better view of one of the main overtaking points whereas stopping midway downhill will let you see more of the circuit. the melbourne hairpin, if it's in use, is a good spot too.
the circuit cafe food isn't great unfortunately, the mobile units can be good but a bit patchy and expensive. i'd recommend bringing your own stash of snacks so you don't need to rely on them - m&s at the donington park services just off the m1 on the roundabout is a good tip for convenience.
other people may have different experiences though!
