The Cleveland Orchestra is absolutely one of the best places to here a concert.
First off, Severance Hall is absolutely gorgeous. It was renovated about 10 years ago and the results are amazing.
The orchestra has really flourished under the direction of Franz Welser Most. I've particularly enjoyed the Mahler and every germanic piece that they've put on for production. You don't need to spend a fortune on tickets either, I could fit in the regular concert on my student budget, and since Severance Hall has amazing acoustics you'll be pleased with no matter what seat you choose.