Half-Life is a unique case where there's not really a best way to play tbh. There's the pre-Steam version with 90s-era features like view roll, there's the modern Steam version that loses those and introduces the exploding crowbar corpse bug but has more modern stuff like proper widescreen and support for the HD models from the PS2 version, the PS2 version has all of the HD models as well but also includes bonuses like animated health dispensers and Decay, Half-Life: Source has a way better flashlight, ragdoll physics, and Garry's Mod content support, but also ruins the anti-tiling texture system, makes the tentacle boss do no damage, and softlocks at the Gonarch, Black Mesa isn't perfectly faithful and makes a good many changes but is a fantastic recreation nonetheless and improves on Xen by far, Sven Co-Op officially includes the Half-Life campaign for free so one can play it with friends if they choose, and there are multiple VR versions depending on if you're playing on Quest or Steam.

It's all very subjective, I'd say the only definitive thing we can say is that Half-Life Source is the worst.