If it has to be a Hasbro version, i'd be biased in favor of Overide GTS. The orange on Overide's face (as opposed to the gold on the Takara version - Nitro Convoy) irks me.
Having all 4 I would say Dark Nitro and Nitro Convoy are the best. But that asside, I find override GTS to be dull, and the orange face on override garish.
Why would you even bother ordering from ToyWiz in the first place? That store - if it deserves such a name - is crazily overpriced on nearly everything it sells. Override, especially the first version, is not that rare a figure that you have to consider the GTS only because it's at retail price! If I were you, I'd definitely consider using the BST sections to get the figure you want. Cheaper in the long run, and without supporting what is in essence the ultimate scalpers. On the figures themselves, I also fall into the crowd of not really liking the mold. Since you have Thunderblast, I think Override would be a good choice just for the clash of colors. GTS doesn't look too bad in robot mode, but is a tad more bland in comparison.
Man, all the Override hate. I agree that the auto-transforming is weak, but she's a great character, the key gimmick is decent, and she's necessary to complete the Speedia collection. I only have the original - couldn't justify buying the repaint since it wasn't a new character. I'm sure I could come up with a neat repaint idea or somesuch, but I've yet to finish the repaints and kitbashes that I have in progress as-is.