I actually found unlocking the characters via VS matches to go quicker than doing classic mode under various conditions. It took only a couple hours with the following steps:
1. Set to 1v1 1-stock survival
2. Kill self 9 matches in a row
3. Win 10th match and unlock match
4. Lather, rinse, repeat until Jigglypuff
1. Set to 1v1 1-stock survival
2. Kill self 9 matches in a row
3. Win 10th match and unlock match
4. Lather, rinse, repeat until Jigglypuff