Hey All!
I have to say that I don't think you NEED a core rule book for T20. The Experience Point chart is on page 35 and I don't think there's anything else that really is neccessary from another book. Maybe I've just played too much d20 and I know the rules well enough. I did find character creation a bit fuzzy, so maybe there is something missing. I do seem to remember Hunter saying that we wouldn't need another book, tho. If I had to pick, I'd go with Star Wars Revised. Actually, I ran an arena game that had characters from Star Wars, Traveller, and D&D in them. They cross over pretty well - all except hit points in D&D - had to fudge that. So go with the Star Wars if you feel you need one. Seems best to me.
Later,
Scout