Which is better for gaming, the 48-inch B5 or the 77-inch A2?

The B5, clearly. It runs at 120Hz with VRR, G-Sync and FreeSync Premium and has four HDMI 2.1 ports. The A2 is capped at 60Hz with no VRR.

Is the 77-inch A2 worth stepping up to over the 48-inch B5?

Only if size is your priority. The A2 wins on immersion at distance, but you give up 120Hz, Dolby Vision, an HDMI 2.1 port and newer software.

Which has better picture quality?

Both are OLED, so both deliver perfect black and wide viewing angles. The B5 has the newer α8 processor and Dolby Vision, so HDR highlights and upscaling are stronger.

Neither has a fixed lifespan, but the B5 gets up to five years of webOS updates through Re:New, while the A2's webOS 22 is past its update window. OLED panels in both can show burn-in with static content.

Can I use either as a monitor or for a bright room?

The B5 works better as a desktop display thanks to 120Hz and four HDMI 2.1 ports, but OLED brightness is modest in both. For a sunlit room, a bright LCD is the safer pick.

Do both support Dolby Atmos?

The B5 decodes Dolby Atmos and has a 2.0 speaker system. The A2 has 20W 2.0 audio without Dolby Atmos, so a soundbar helps either set.

LG B5 Series OLED 4K TV (2025) vs LG A2 77-inch OLED TV

Buy the 48-inch B5 for a bright, fast, modern set: 120Hz, four HDMI 2.1 ports, Dolby Vision, G-Sync and FreeSync, and the newer α8 processor. Buy the 77-inch A2 only if sheer screen size at the lowest OLED entry point matters more than motion and gaming features. The B5 is the better-built, better-supported TV; the A2 is a 2022-era 60Hz panel with three HDMI ports and a weaker processor, and owners of that generation note dimmer HDR and no 120Hz gaming.

Choose the LG B5 if you sit within about 6 to 8 feet, game on a console or PC, or want Dolby Vision and four HDMI 2.1 inputs.
Choose the LG A2 if you sit far back in a large room and want the biggest OLED picture for movies and streaming rather than gaming.

Prices

LG B5 Series OLED 4K TV (2025): $299.99 at Best Buy (checked today)