I have a theory why the Sheffield derby (the one vs Wednesday) is the most important to both sets of fans in British football.
1) both teams actually from the same city / town
2) both teams historically very evenly matched
3) both teams are unlikely to win a major trophy, and very rarely compete in games of great significance (eg no cup finals, no European football), so the rivalry assumes greater significance as no other ‘distraction’.
4) both teams are incredibly well supported given the recent lack of success and Sheffield being a two-team city.
5) United & Wednesday often find themselves in different leagues so a derby between the two is a comparative rarity.
Taking the other derbies which could compare;
1) Liverpool / Everton
Both sides are historically fairly evenly matched (if not recently), however, Liverpool play many games a season of greater importance than their derby game versus Everton.
2) Man United / Man City
Again, a fairly even match up in terms of success and history. But both sides also play games of greater significance during the season, such as cup finals and European football.
3) Celtic / Rangers
See above
4) Spurs / Arsenal
See above
5) Chelsea / QPR / Fulham / Brentford
Chelsea dominate in West London and so there is not the feeling of significance of these derbies to both sets of the fans. I’m sure it is of great importance to the likes of QPR and Fulham, but probably not much difference to any other game for fans of Chelsea?
6) West Ham / Millwall
See above, one side historically dominates the other so they’re not evenly matched.
7) Forest / Notts Co
See above, Forest dominate
8) Bristol City / Rovers
See above, City dominate
9) Birmingham / Villa
See above, Villa much the ‘bigger’ team
WBA v Wolves / Newcastle v Sunderland / Ipswich
The only other 2 derbies