I would say Ohio State is obviously the best Big Ten team since 2000 (arbitrary starting point but so what). A national championship and five BCS bowl wins, as well as the third-highest winning percentage nationally over that stretch is pretty darn good. No debate there.
After that, it's not pretty. Penn State has two BCS wins but their reputation has obviously been torpedoed with the JoePa saga. Wisconsin's three straight Rose Bowl losses were a big fail. Nebraska has continually slipped up on the national stage and were doing that even before joining the conference. No explanation needed for Michigan. Michigan State flies under the radar a bit and has improved drastically since hiring Dantonio, but the seasons under John L. Smith were lost years basically.
As it stands, the conference desperately needs Michigan and Penn State to return to their winning ways. I essentially see Wisconsin and Nebraska in the same boat despite taking different roads to get there. Their success would be nice for the perception of the depth of the conference but it's not absolutely necessary. Michigan State looks primed to ascend to a top-tier team and are acting like it; go check out the kids Dantonio is pulling in.
Basically I believe the future of the conference lies in the East teams regaining their former stature. If the top West teams can contribute, great. But the conference has a Michigan and Penn State problem, not a Wisconsin and Nebraska problem.