Stanley is the lowest tier of SBD lineup (S < B&D < Dewalt).

Circ saw is basic tool not worth spending too much on it if you don't use it that often. Stanley RM289 for that price range I'd get a GKS140 1400W instead at few bucks more https://shopee.com.my/product/29050559/5058539120 or the Makita MT5801.

IMO a cheapo tool with good blades (branded blade like bosch T80 fine cut) can do nice cuts. Eg. RM149 1300W Okatz seem very popular https://shopee.com.my/product/11272182/4844194808 .. the only thing is the blade guard seem to be plastic (not metal) cost cutting? at work I remember abusing the shit out of the cheap Okatz jigsaw and a few Bosch blades for cutting many plywood sheets and it worked great

In terms of motor size, a bigger motor can cut hardwood like balau or plywood easier (faster) without bogging down. If cutting pine or softwood only, no issue for any saw.

For blade size the 7in (184mm) blade is common and cheaper than the 6in ones.

That is in the US 

Dewalt, Stanley, and Black and Decter are all under Stanley and Black & Decker.

Dewalt bought by Black & Decker long time ago. Later Stanley merged with Black & Decker to be call what it is now.

I own Stanley circular saw for reason of warranty cover. 

Dewalt - 3 years
Stanley - 2 years
Black & Decker - 1 year

As for my knowledge, Stanley is hot brand. Many companies want to sell their products under Stanley name but of course you will have to agree with Stanley term. For example, Stanley water-jet washer are from many other companies over several years. Now it is actually a product from an Italian company called AR Blue Clean. You'd be surprised that the warranty for similar model is only 1 year from the AR Blue Ocean but 2 years if you buy Stanley re-branded one 

I'd say probably just buy any known brand that is most convenient to get service from just in case you need one.