Problem is that the most important thing is fit. Hard to tell that online, especially if it’s your first road bike. Same goes for handling and responsiveness.
Can’t see any mention of mudguard eyelets on the Mekk; the others both have them on the frame but seemingly not on the fork, which is a shame. The Merlin has rack mounts, too.
Other than that they all seem much of a muchness. The components will all be broadly adequate and the wheels will probably be a bit lardy and under-tensioned. If you ask me the Mekk looks a bit cheap, so I’d go for one of the others on aesthetics, but there you go. Maybe find some reviews if there are any, and see how they rate the frame.