For sports that are not the most professionalized (tennis, etc), you can be viewed the best of the profession if you win the World Championship, Olympics, or World Cup. Which title is the most prestigious? Perhaps "difficult" is the more objective and appropriate word than "prestigious".
About the difficulty in winning a title in one's finite career, one needs to consider the competition and format in an event and how often the event is held. Olympics is once every four years. World Championship is variable, usually once every one or two years. World Cup (not the FIFA variety) is typically once a year, and some sports don't have it. As anyone will compete in fewer Olympics than Worlds or Cups, the gold medal is more desirable personally. Not to mention that your gold medal will count towards your country's totals, whose significance is dubious.
Obviously, if you want to win it badly, you will try hard. On the other hand, how stiff the competition is also impacts whether you win it or not. This is where Olympics is not technically the hardest. Both Olympics and World Cup severely limits participants, so sometimes the top players (e.g., from the top 8) are left out. It is debatable that the pre-selection process should be considered as part of the events as well, but it disregards the non-trivial timing of players' peaks. Also, because upsets happen all the times in sports, winning an Olympic involves a higher degree of luck. The World Championship typically has 128 players in the main draw, like GS in tennis. Essentially all the top players are present, so this is the most difficult event to win. In sports like table tennis, many players enter multiple events like singles, doubles, and mixed doubles, which take place at the same time. This is serious stuff, as in the final, you are probably far from your best physically. In Olympics and World Cup you are less affected by that, playing higher ranked opponents from the beginning notwithstanding.
So I think winning a World qualifies one on top of the profession better than the other two titles, even though its honor might not be as high as that for a gold medal for casual viewers.
The purpose of this blog is to slightly knock down Olympics and to set a standard to compare players.
For example, Wang Liqin, Ma Lin, and Zhang Yining were not selected to play in 2000 Olympics, even though they were already quite good then, with Ma and Zhang coming second in 1999 World. Wang and Ma were the best male table tennis players from 2001-2008, while Zhang is one of the best female players of all-time. Xie Xingfang played in only 2008 Olympics, while in 2004 she was already one of the best badminton players. There were legitimate reasons that they didn't qualify, but the real issue is the Olympic quota. If some of the very best players can't compete, how representative and strong can the field be?
As a result, a gold medal has to be taken with caution, not to say that the winner is not worthy. Take Ji Xinpeng, the winner of 2000 Olympic Badminton. He played the best tournament of his career, beating the three other best players in the world at the time. So he absolutely deserved it. But he hardly won anything else. If you are the best in only one event, no matter how prestigious the event is, you may be the luckiest, but not the best of your profession. Yoo Nam-Kyu, the 1998 table tennis gold medalist, is in the same category. And he didn't beat any apparent top players at the time, and he didn't have any major, good results before or after. Ryu Seung-Min, a better player than Yoo. He beat an old Waldner and a nervous Wang Hao in 2004. He got better results in the Worlds and Cups than Yoo, although never winning. The accomplishment of Ryu is probably slightly ahead of that of Werner Schlager, winner of 2003 World but nothing else, both below Timo Boll, the two time World Cup winner.
A problem with the overemphasis on Olympics is that players who barely miss out qualifying or winning it lose motivation fast. Wang Hao lost in two finals, and after winning the 2009 World, he has no other goals except the 2012 Olympics, but he will be "old" by then. Xie Xingfeng lost interest completely after 2008 Olympics, as she had won everything else, often multiple times, and by 2012 she will be too old. They should be considered better players than some of the gold medalists, despite not winning the most prestigious honor in many people's views.
An interesting issue is how to compare Wang Liqin and Ma Lin. In terms of teams and doubles competitions, both are excellent to similar extents. In singles, their head-to-head is about equal, and Wang won three Worlds, Ma four Cups and one Gold, all records since 1980. Winning three Worlds is definitely more difficult, but is Wang better? Well, Ma is probably the most unlucky player ever. He lost in three World finals, all in close contests, all having good chances of winning. In addition to luck not coming his way, Ma was likely affected by playing too many matches in Worlds (doubles, mixed doubles, etc), as his style is more demanding, and Wang is naturally a physically stronger player. This can explain why Ma performed better in World Cups and the 2008 Olympics.