Which is a better soil for foundations, alluvial or aeolian?

Alluvial soils tend to be more compact and therefore have a higher bearing capability. Since aeolian soils are deposited by the wind they tend to be less compact.

I base this on my experience in West Texas where there is a lot of wind blown sand. When we were designing and pouring foundations we usually had to allow for about 18 to 24" of what was called "blow" sand. It was loose and unconsolidated.

Is aeolian type of soil? when do foundation on alluvial soil, you need to do proper treatment and make the design to prevent sliding and reduce water content in the soil

Alluvial is probably "better", but neither are very good. To build on either one, you'll need a foundation which is designed for very poor soil conditions.