Its a tricky one and I agree some shine others well are terrible! That said I think the W brand itself can really divide opinion even with people who like the W brand as they are so subjective!
W Punta de Mita is far superior to Vieques away in my opinion
W Bali is amazing, the staff as much as anything!
W South Beach if you get the right suite is stunning, but realise this one will divide opinion but we have always found the staff to be really good!
W Doha was really good after issues at checkin, but the staff were great as was Spice Market. The design of the property is pretty good to!
W Maldives once would have made this list so easily but it has just had to many wrong GM's and not enough investment!
As for the worst well, W NYC, it might be the original but it is the only hotel I have ever sworn never to return to!