These two get compared constantly, and for good reason — Dulux Heritage was built to chase F&B's heritage look at a friendlier price. Both are proper paints. The question is what you're paying for.
Farrow & Ball has the deeper bench: 301 colours against Heritage's 112, with serious strength in greens (67 of them) and blues (41). The finish is the real differentiator — that flat, light-eating, slightly chalky surface that shifts through the day. Colours like All White read clean and crisp, and the pigment density means even a pale neutral has somewhere to go in changing light. The LRV range runs 5 to 92, so you get genuinely deep darks and genuinely bright whites.
Dulux Heritage is the value play, and it's a good one. The palette is leaner but well-curated — 27 neutrals and 26 whites, which is exactly where most people are buying. Indian White and Panel White are lovely soft off-whites that hold their own next to anything F&B offers in that range. Heritage's LRV range is 3.7 to 86, so the darks go a touch deeper than F&B's, and the wipeability of the Diamond Matt range is frankly better for kitchens and hallways with kids about.
The honest take: if you want a saturated, characterful colour — say F&B's Acid Drop, a zingy green that simply has no equivalent in the Heritage book — go Farrow & Ball, because that's where their range and pigment depth earn their keep. If you're after a calm neutral or off-white across a whole house, Heritage gives you 90% of the result for a lot less outlay.
My practical advice: order sample pots of both, paint A2 boards, and live with them for a couple of days on different walls. You'll often find Heritage nails your neutral while F&B wins on the one feature colour you actually care about. Mix and match — there's no rule against it.