Lemlist's calling card is per-prospect personalisation — dynamic images with the recipient's name, video personalisation, image-in-email tricks. It's the right tool when each send deserves a few minutes of human thought and the campaign is small enough that craft compounds.
Instantly is the volume tool. The cleaner UI, the better-out-of-the-box deliverability defaults, and the inbox-rotation primitives all favour teams running thousands of sends a day across many domains. Personalisation is functional but isn't where it shines.
Many of the outbound teams we work with end up running both — Lemlist for tier-1 named accounts where craft matters, Instantly for the broader volume play. If you're forced to pick one, pick by daily send volume per SDR: under ~80/day favours Lemlist, over that favours Instantly.