Both have 2 queens + sofabed so they offer the same sleeping options. Wondering also about the difference in breakfast options? Both offer hot buffet, has anyone stayed at either and able to comment on quality of buffet?
Unless you opt for a studio room at the Residence Inn, though, your two queens will be in a fully separate bedroom, whereas the Springhill only has a half-wall between the "sleeping" area and the "living room" area.
We stayed at the Residence Inn SeaWorld for 7 nights over Christmas week. We were very satisfied and would not hesitate to stay again. There are tons of pictures of the room and the hotel amenities in my trip report (click on the link in my signature).
Breakfast at the RI was excellent. Daily they offered two different types of muffins, bread, various flavours of bagels, yogurt, oatmeal, fruit salad, several different kinds of cold cereals (four, I think), milk, juice, coffee, tea, about 6 different sodas (for breakfast?!?

) and hot chocolate. In addition to those daily items, several days they had scrambled eggs, sausauge rounds, home fries, shredded cheese, warm biscuits, and sausage gravy. Other days they had pancakes, sausage rounds, buscuits and gravy. There was also french toast at least once. Food was plentiful, seating was always available (even during the super busy holiday week), and the breakfast staff were wonderfully friendly (as were the front desk staff....top notch all the way).
Another big difference between the Springhill and RI ..... you will have a full kitchen at the RI where you won't at the SHS. We LOVE having a full sized fridge when on vacation.