Clip less is ideal for gravel. But picking the SPD shoes should be based on the type of riding you do.
If you do regular bike packing, touring, hike-a-bike or commuting then pick a pair of shoes that are decent to walk in.
Or if you do racing of some kind like cx, gravel or even xc then pick a pair that are stiffer and lighter.
Or if you just ride a bit of everything then there are shoes that are pretty stiff yet you can walk in. I have a pair of Shimano ME5 which despite their enduro leanings have been great and have been used for long days in the saddle riding in highlands etc
Edit: both Shimano spd and Time Atacs are great, not much to pick between them.