We ALWAYS sit for Spectro. Granted, you have to get there early and stake out a section of curb, but you have to show up early for good seats at Fantasmic too. Difference is waiting for Spectro, you get to sit. Waiting for Fantasmic, you have to stand until they open the theater. So I wouldn't base a choice on this.
As I said earlier, Fantasmic is the better show but I'd try to see both if possible.
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