My personal favorites are the first one I followed entirely (1998) and the one I actually went to (2014). Can't talk about the previous ones so I'll just leave a little summary:
1994 - I only remember watching the whole final, which wasn't a great match. Some great surprise teams out there (Nigeria, Netherlands, Romania, Bulgaria, Sweden) altough after Germany and Argentina were out it seemed clear that this was Brazil's to lose.
1998 - Great tournament overall with fantastic talents and a lot of unpredictability: easily 6 of the 8 teams in QF had a decent chance of winning the whole thing. Denmark's last dance and Croatia's cinderella story were great. The final was underwhelming tough.
2002 - Really weird tournament, with poor refereeing, some of the favorites dissapointing (NT and clubs schedules collided a lot at the time and lots of big names were injured or exhausted) and a deserving champion but one that also had a dream fixture, which included Germany losing its best player for the final. Triple R tough
.
2006 - Now that's a good tournament with most of what we want in a WC. Brazil's big four, Zidane story, a fantastic Argentina squad, a very entertaining and young German team. Didn't care that much for Italy tough. They did keep calm at the most crucial moments (unlike Zizou), altough poor refereeing help them surviving at earlier rounds.
2010 - I really dislike this WC. Vuvuzelas + the awful Jabulani + a freaking octopus being the center of attention. Spain's Tiki Taka prevailed, but they didn't face a big challenge the whole tournament (maybe unfinished Germany in SF) and still struggled from beggining to end. Mention to Uruguay's great run and to that match with Ghana.
2014 - Extraordinary tournament, exciting from beggining to end. Maybe the best group stage in modern WC. Elimination rounds had less flair but a lot of tension (Brazil-Chile, Germany-Argelia, Argentina-Switzerland, Mexico-Netherlands). Plus the 7-1, plus a great champion, plus an exciting final (I don't know why some remember it as a boring match. It wasn't).
2018 - kind of dissapointing to me. The level wasn't bad, but most teams played exactly the same which didn't lead to a lot of great matches (Russia-Spain, France-Argentina, Belgium-Japan and England-Croatia come to mind). Half the goals were VAR penalties or own goals which didn't help either. The final was a cakewalk for France since Croatia was knackered.