I use Shopee (new parts) and Carousell/Garage Sales for used parts. In Shopee, I only check out a few shops like EtechPC, PC Byte, NetStore, and a few more other shops.

For in demand items (i.e Ryzen 5000 series and RTX3080), most if not all Digital Mall & Lowyat stores will require you to bundle with other items (ryzen CPU with motherboard and 3080 with full build mostly), very rarely do you get to buy these items standalone, unless you have good standing with them.

If you're not hunting for these hot items, then there isn't much difference between physical and online stores, other than peace-of-mind and speed. Shopping at physical stores can get you some discount if paid in cash, but some stores also charge "vendor fees" for using credit card (at least this was the case when I bought my PC from Digital Mall 5+ years back). Also worth bearing in mind there are 0% installment options for online purchases, which may be a plus to some buyers.

Some more reputable and large vendors are Thundermatch (changed name recently to TMT), c-zone and Aone Plus (all three stores are in both digital mall and lowyat plaza I think), and also All-IT Hypermarket at the top floor of digital mall.

I suppose there is no harm to shop physically first, then if prices or conditions are not favourable, you can always get them online. Happy hunting 

I stay nearby Digital Mall so I'm biased lol

Lowyat Plaza is bigger so it might have more variety and more things in stock, Digital Mall is basically a smaller version of Lowyat cause most retailers in Lowyat also has branches in Digital Mall

Word of worning, don't get ripped off cause they might try to hardball you if you are clueless about tech/pc parts, and especially cause you're a foreigner