Your marketing site and your product are two different jobs
Most SaaS companies hire one firm for both and get one done well. The disciplines look adjacent and are not, and the split runs right through this list.
A marketing site is a persuasion problem measured in conversion. It rewards distinctive visual work, clear positioning and a fast path to a trial signup. Iteration is cheap and the whole thing can be rebuilt in six weeks. basement.studio, Focus Lab and Superside all live on this side.
Product UI is a comprehension problem measured in activation and retention. It rewards patience with edge cases, permission models, empty states and the fourteen screens nobody demos. Mistakes compound, and rebuilding is expensive because users have learned the old version. Eleken, Cieden and Fuselab sit firmly here, and Eleken will tell you outright it does not do the other side.
A few firms genuinely cover both. Clay, Mission Control, Metalab and Lazarev run brand and product together, and for a company where the two have drifted apart that integration is the whole point.
Decide which problem you have before you shortlist, because a studio hired for the wrong one will do competent work on something you did not need.