Of your two choices, Lake McClure is by far the best. It has an arm that runs several miles up to the Bagby Bridge. A senic run that is quiet and pieceful. If you plan ahead, there are several campgrounds with a wonderful view of the lake.
Don Pedro is one of my favorite lakes, but the campgrounds can get to be a Zoo. Both sides of the lake.
I have camped at McClure and made a day trip over to Don Pedro or New Melones from there. New Melones is a secret lake we don't tell anyone about. It is FREE and has a long arm that has great scenery(sp). Not that good for camping, but great for boating. All three of these lake are with-in about 25 miles of each other. Go buy the "Califonia Lakes" book and check out the possibilities. Camping World has them, along with other places. Have fun. Al