My original goal size was 8mm as I found most of the plugs and tunnels I liked started at this size.
Then I decided my goal size would be 10mm, after seeing my ex hit that size and really liking how it looked.
Now I think that 8mm and 10mm aren't really that big at all, so my goal is 12mm.
I don't think I'd ever change my mind again though, I don't think I'm a person who could pull off a larger size and a lot of the jewellery types I like stop at around 12mm-ish.