I am a huge of a big ten team and I still would rank the big 10 below the SEC for the last 10-15 years because of the number of quality teams the conferences have had in that time frame. The only thing the Big ten has over the SEC is that the bottom feeders of the big ten are better than the ones in the SEC (Vanderbilt is never going to beat florida or LSU or ohio st./mich for that matter, but it wouldn't be a surprise to see a Northwestern beat a Michigan) But to answer the question you have to look at the number of teams that have a legimate chance to make a run at the national champioship every year.
SEC
1.Auburn 2.Florida 3.Georgia 4.LSU
5.Tennesee
Big ten
1.Michigan 2. Ohio St. 3. Penn st.
Then you look at teams that will have a great season every few years.
SEC
1.Alabama 2.Arkansas 3. S. Carolina
Big ten
1.Iowa, 2.Michigan St., 3.Purdue, 4. Wisconsin
(Miss st., ole miss, vanderbilt, kentucky, minnesota, illini, indiana, NW are all bottom feeders and all belong in the pac 10.)
My Conference Rankings by legitimate power houses year after year
1.SEC (Auburn, Florida, Georgia, LSU, Tenn.
2.Big 10 (Michigan, Ohio st., Penn st.)
3.Big 12 (Nebraska, Oklahoma, Texas)
4.ACC (Florida st., Miami, Va tech)
5. Big east (W.Virginia, Louisville)
6. Pac 10 (USC)