As above, it depends what sort of thing you after and if you want daylight or artificial light.
The only problem is that all the nice scenic places will be full of people on their days out during the day. I reckon That Perch rock will be good if you can get a good spot. Ive also used the Arrowe Park carpark by the cherry orchard during the day.
I always take pictures at night in artificial light and by far the best place around here, and i think many will agree, is the new candy in bromborough way. The lighting is spot on there.
Theres also a spot at the end of Meols/Hoylake where theres a small car park with a few boats in. The light isnt great though and it can come out yellowey but if you set the camera up right you can get some good pictures.