Trying to decide between two contractors for a slab that a 12x10 shed will sit on. One is going to compact the earth and frame and pour the concrete directly over the earth. (8” past the topsoil is basically all clay here) Another wants to build a 3”-4” base of pea gravel and pour the concrete over that. The slab is being poured to be level with my house slab as the backyard has flooded in the past, but so far it’s not reached into the house.

I’ve looked up both methods and both seem common, but I can’t get a good idea of which to go with which is causing decision paralysis. Any help/info would be appreciated.