As with many things, it depends on your own preferences/situation....
we have done both, and find that the QSDP works best for us. We only do one or two TS meals during our stay, and we don't like to get bogged down by being tied to ADRs every single day. We also tend to eat at the most expensive counter service restaurants (like WPE and Tangierine Cafe). For us, I priced it out and it's worth it. IT's not the best deal ever, but we save a few dollars each day (don't forget to count in tax when you are pricing things out on the menus) and don't have to worry about every little thing while we are there. The kids are always bugging me to get a resort mug and various snacks, and now I don't have to say "no" all the time!