I go to Scotland with this very forum in early May, but if I had another choice of where to go in early May I would certainly choose the Mediterranian like in Calgary, Sardegna.
The town is smaller than the other options but it is rather old, going back to the Phoeniciens. I have been there twice and I will sure go back there: The churches, the botanical gardens, the University, the steep small streets, the food (esp. the world unique sweets). And if you rent a car and drive within an hour around you find the wildest blooming exotic places, edible cactus fruit, herbs of any kind, cliff coast with bathable bays by their feet, the bluest ans turquoisest of waters, abanodened mines, Morisco leftovers ... for beverage try the unique "Mirto" and do not miss some of the greates seafish restaurants in the world...
I have not yet been to Lisbon and like pretty much what I have seen in movies and photos, so...