Yes it has been asked several times in the last few weeks. It basically depends on the user, there are many opinions as well as scoops.
Stainless equals longer lasting and durability
Aluminium equals lighter weight and ease of use on long days.
As already pointed out an aluminum scoop with a stainless lip will give longer service than just aluminum. It all depends on the type of hunting you will be doing and the beach conditions.
If your going to hunt in the water you need a bigger mouth scoop. Reason: you want to try to get the target in the first scoop if possible, or as few scoops as possible. On a good sandy beach that is not rocky, an all aluminium scoop will give years of service.
It all boils down to 1. type of beach conditions 2. type of hunting 3. how much money you are willing to spend. 4. how much weight your willing to drag around 5. are you going to travel with it (ie) airplane, if so travel model to take apart. 6. Wooden handle, Fiberglass handle, Aluminum or Stainless
Many avid beach detectorist have more than one scoop and depending on where they are going to hunt decides which scoop to take. in the water or on the sand or at a particular beach that is full of rocky areas.
I use
RTG Aluminium
Nuttall Diamond Head
BCOOP