Best - italia 90. I remember watching the cup final that year which ended 3-3 with a certain Ian Wright scoring 2 and I as a 7 year old youngster just got interested enough to watch the World Cup that summer. The rest as they say is history. Pavarotti, England actually doing well, gazzas tears, Cameroon winning the hearts of the world etc Got me hooked on to the sport.
Worst - more difficult choice this. Contenders are USA 94 or South Africa 2010. I'd have the 2002 one as well but that Brazilian side was awesome. England not being at USA 94 meant it had to go some to gain my interest still being just a kid then. Yes it holds the world cups greatest ever goal by Al Owairan for Saudi Arabia v Belgium and also Romania v Argentina and Brazil v holland but the rest was terrible. 2010 has possibly the worst winners of a World Cup ever, scoring the least goals and a big reason why tippy tappy is so prominent these days and also why football is so boring. If I had to choose, I'd go 2010