Here is some advice on the correct spacing of inverted U (or Sheffield) racks.
They are often placed too high or low, too close together, too close to a lamp-post or wall. You need sufficient room at each end for a large wheel to stick out. If the ground is not level, then they are best placed along the contours to prevent bikes rolling when locking up.

The location should avoid any natural pedestrian route, fire exit route etc.

The stainless steel ones are better than rough galvanized steel.
Fancy designs generally work less well.