The chains most consistently in this category: Motel 6, Super 8, Days Inn, La Quinta, Red Roof Inn, Hyatt Place, Holiday Inn Express, Sonder, and Pod Hotels. The chains most often not in this category: Hilton (most brands), Marriott (most brands), full-service IHG, Drury. Best Western, Wyndham, and Choice are mixed at the franchise level.
Independent boutique hotels are wildly variable — some are aggressively young-guest-friendly (city pads near campuses, micro-hotel concepts, art-focused boutique brands), and some are 21+ flagships in luxury markets. The directory filters this for you.