In November 1911, Capablanca challenged the World champion Lasker. Lasker replied with 17 conditions. Some of these conditions were that the match should be for the 1st player to win six games, draws not counting, and to consist of no more than 30 games in total.
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This one is from a different site. It looks like the tournament debate has been going on for 90 years!

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The World Chess Federation (FIDE) was founded in 1924. When the reigning World Champion Alexandre Alekhine died in 1946, FIDE took over the function of organizing World Championship matches. Before that time, sitting champions had been somewhat capricious in determining against whom and on what terms they would accept a challenge match. FIDE also assumed the role of awarding the titles Grandmaster and International Master, as well as eventually assigning numerical ratings to players.

In 1993, in the middle of a cycle of matches to determine the World Champion, Garry Kasparov and Nigel Short broke with FIDE to organize their own match for the title. They complained of corruption and a lack of professionalism within FIDE, and formed a competing Professional Chess Association. Since then there have been two simultaneous World Champions and World Championships: one extending the Steinitzian lineage in which the current champion plays a challenger in match format (a series of many games); the other following FIDE's new format of a tennis-style elimination--or "Knockout"--tournament with dozens of players competing.
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If that's the state of it nowadays, I'd say it would be best to leave it to the creator or organizer of the games or tournaments. Sounds like ol' FIDE is still messed up. Maybe that's why I stopped playing Chess 30 years ago. I'll get the links:
http://www.chess-poster.com/great_players/capablanca.htm
http://www.campusprogram.com/reference/en/wikipedia/c/ch/chess_1.html
There's lots more, but it looks like a history lesson that's still ongoing. I used Google with these words typed in to search.
"six game match" chess tournament
They also talk about IBM's Deep Blue program which also had a six game match involving Kasparov. Though they only played six games, draws counting.
Sounds like both methods work.