Yes, I have played both. Merchants every time, as for me Mansions is awful. Very little replayability due to a limited number of scenarios (fan fiction could help here) and limited monster types, no control over where you go and far too much luck (apart from me failing 12 rolls on the bounce with a 6/10 chance of success in most of these - and a colleague failing 3 9 in 10s in a row) in a type of game where this should be low. We spent 45 minutes looking for the first clue, about 2/3 of the cards we revealed were "you find nothing of interest". Any investigator would have walked out the front door, which is what we did. The biggest disappointment I have ever had as a gamer, and I intended buying the game beforethe session when I played it. Perhaps it is playing CoC for close to 25 years that made it a big let down.
Merchants is good fun with a good flavour and attractive game board. Perhaps the biggest criticism that seems to be levelled at it is that it is too hard to win as a pirate, although you probably have to get some ship adds first. An experienced player would kniow when the game *should* finish which may also be a limiting factor. It's a good laugh though.