We upgrade when something happens to force it. We started with Suunto SME/MLs which I think was close to their first real dive computer. They had to be sent in to change the battery. When UPS lost our computers on the way back right before a trip, Suunto kindly sent us a pair of their latest model, the Solution, then told us we could keep the new ones. (Really good customer service back then!) Then we did Nitrox and got Vypers, using the Solution as a backup and sometimes doing pretend deco stops just to keep the air-only backup happy. When that got old, we dumped the Solutions and got Gekkos for backup. We're still diving with those models, having bought 1-2 of the same used along the way to replace something that got flooded.
That early free computer experience kept us loyal to Suunto for awhile. Might have moved to some other computer line by now, but we've currently got 5 of these. We're used to them and they do the job, so it's hard to justify spending a bunch upgrading. But one of these days I will get tempted by a pretty display. Or maybe by a battery door that's not such a PITA.