Best for mostMeredith McKinney · 2010
Meredith McKinney's 2010 Penguin translation is the one I'd start with — clear, natural modern English that still carries Sōseki's quiet melancholy. It reads easily for a contemporary reader without flattening the book's restraint, and it comes with a helpful introduction. This is where I'd start.
The classicEdwin McClellan · 1957
Edwin McClellan's 1957 translation is the celebrated classic — chosen for UNESCO's collection of representative works, and the version that introduced Kokoro to English readers. It's more formal and measured than McKinney, which some find fitting for Sōseki and some find a little distant. The traditional choice.