I have only had experience of Giant, a wheel problem and then a cracked NRS frame (A known problem with earlier models apparently)
In both cases, Giant’s warranty team were excellent. Outstanding, even.
The wheel was a cracked rear hub body on a DT hub. They immediately swapped the whole wheel for a rather trick, team issue 24 spoke tubeless rear, with a free tyre thrown in for good measure.
Frame was a known problem. Rang them on a Monday, dropped the bike off on a Tuesday, had a fully rebuilt, brand new frame (With new headset, BB and shock) in my hands by the Saturday.
Impressed. Very impressed.
I also happen to know that one basis on which the Surgery choose brands, apart from supply and price considerations of course, is after sales care. When you sell that many bikes, it gets to be pretty important. Giant are one of the best out there, IMHO.