Caesarstone and smartstone are the same product base, which is quartz. Read both websites to get more information. Depends what colour you are after, may decide which product you get.
Also, there might be a price difference that will help you make up your mind.

Just want a great product which doesn’t attract stains & water marks.

cost will not make me to choose a poor lesser quality product

Any bench top needs to be cleaned, both will have water marks and stains, if not cleaned as soon as possible. Always use the cleanser products available from the quartz companies.

They are the same as they are both engineered. From the builders perspective the smart stone comes in bigger slabs so it will save on costs to buy fewer slabs. He is trying to save you or himself money. Ceaserstone has a wider variety of colours, there customer care is top notch and they have more product. Like with any Bench top be it laminate, stone or marble, as soon as you drop something on it, clean it up.