Toontrack treats existing customers like crap and tries to fleece them. I got rid of everything I had from them , which was quite a bit. I despise them.
I'm not sure Melda counts as a large software developer, but I'm a Melda fan and love their upgrade model. As for upgrades, though, "lifetime upgrades" become less useful when they elect to create new, tangential products of the same type and put new features there,
Eventide has always been generous, fair, and awesome.
UVI is attentive and solid, although their upgrade pricing for sound libraries leaves something large to be desired.
NI is generous but their customer support is hideous.
IKM is a mixed bag but continues to run with some bad decisions and lacks nuance as to what is owned, upgrades, etc. That said, they generally offer great value for money.
WUP is a joke, so Waves gets no love here. Their products and and pricing are generally good. Their installers and endless re-versioning are a joke.
Ableton has great support and kit but massively overcharges existing customers.
I'm new to Arturia but they seem quite decent.
AAS is super generous with customers and very responsive with support.
Plugin Alliance has historically been great across the board with support and generosity. Not as big of a fan since the model changed.
Unsure if U-he is considered large, but they are great in every way.
I would have given Cakewalk high marks, but the Lifetime Platinum screw and subsequent decommissioning of everything not CbB burned my ***** something fierce.