It depends on how you play: Game Pass usually wins for players who try many different games and love day-one releases, while buying — especially cross-region at deep discounts — wins for players who only finish a handful of titles a year and want to keep them forever.
The subscription math is simple: Game Pass costs a fixed amount every month whether you play or not, and games leave the catalog. If you genuinely play several catalog games a year and would have paid for them, the subscription earns its keep. If you mostly replay favorites or play one big game for months, those subscription fees quietly exceed what buying would have cost.
The buying math has a multiplier most players ignore: regional pricing. A title that looks expensive locally is often 50–90% cheaper in another Xbox region, which means a patient buyer using region comparison and price alerts can build a permanent library for less than a year of subscription fees.
The smartest approach is usually hybrid: keep a subscription during months packed with releases you want to try, cancel it during quiet stretches, and buy the games you know you'll keep at their cheapest global price. XBX SPY handles the second half — compare every region, watch the price history, and get alerted the moment your target price hits.