best buy is probably a better choice in terms of who would know more about how to fix them. After all, Best Buy has a trained personnel who is meant to deal only with this stuff, so I would assume they would be your best et. Though I dont know the cost of it at Best Buy.
If they are unable to fix it, you should send it into Nintendo. It may be costly, but you can be sure they will get the job done right. It follows the "quality over quantity" concept. You can either pay a cheaper cost for a halfassed job that will make your Wii work for awhile only to need to get repaired again in a couple of months, or, you can pay full price and ensure it gets fixed entirely.
Like I said, your choice.
Glad I could be of assisstance!