I've done a little research recently and i will show you results. I was curious what domestic league was the best through the years. Of course from the XIX century to, i think, at least forties of XX, English league was the best league in the world without any doubt. But then? European cups gave us possibility to compare the strength of clubs from various leagues.
Each winner of any major european cup gave his country 4 points, each second place team - 3, semifinalists - 2, quarterfinalists - 1. Then i sum up points from 5 last years. I was interested in 5 top leagues every year. Results for English league are as follows:
1956-57 - none
58-59 - 5th
60 - 4th
61 - 3rd
62-64 - 5th
65 - 4th
66 - 3rd
67 - 2nd
68-69 - 3rd
70-75 - 1st
76-83 - 2nd
84-86 - 1st (we should remember that in this period ban started)
87 - 3rd
88 - 4th
89-94 - none
95 - 5th
96-97 - none
98-99 - 5th
00 - 4th
01-03 - 3rd
04-05 - 2nd
06-07 - 3rd
08-11 - 1st
12 - 2nd
If it wasn't for that ban from European cups, English league would be still the strongest for a couple of years.