If you are flying UA SFO-TPA NS vs. SFO-MCO NS, a quick single peek into United search engine (for me at least) shows SFO-MCO more expensive (~$500 RT) than SFO-TPA (~$425 RT).
For me out of LAX, I see LAX-MCO NS @ $292 but there's no non-stop to TPA, so LAX-SFO-TPA RT is $404.
Good luck!
David