Depends what you're looking for.
For food, my best ones are Italy, Spain, France, Portugal and Sri Lanka. Worst probably Germany and Canada. (Although Canada did introduce me to the sushi burrito.)
For people, the best are Italy, Spain and Canada. Worst: Morocco and South Africa.
For weather, the best are Italy, Spain and Costa Rica. Worst would be Scotland, Germany and Canada (in winter).
For natural beauty, the best would be France, Costa Rica, Sri Lanka, South Africa, Scotland and Ireland. The worst, probably Morocco. The parts of Canada and the USA I've visited have been pretty underwhelming too, but I haven't seen much of either country.
For hotels/places to stay, the best have been Scotland, Portugal, Costa Rica and Italy. The worst would be Morocco, USA and Canada. Sri Lanka not great either. Canada (Toronto and Ottawa) gets a special mention for being INSANELY EXPENSIVE and really not that good. (Spent the last few days in a "budget" hotel in Toronto which cost around £150 a night and where breakfast was barely edible and eaten with paper plates and plastic cutlery!!!)
For culture, best are France, Spain, Ireland, Scotland, Italy and Sri Lanka. Don't really have a worst.
Overall I think the standout best are Italy, Spain, Scotland and Costa Rica. Worst would be Morocco, and I didn't really rate Thailand either.