I mostly choose the middle bottom or middle upper. 1st - because it's closer to GO/Next button, and i have to travel less with my mouse, and 2nd - because it mostly contains R girls i like more of all R cards that i can get on Ngacha, like Suzuna Hanamiya, Mayumi Takasaki, Aya Kitagawa, Yumeho Suzumi, Ai Naruse, Fumi Annei and others. Also, the middle bottom more often contains SR cards for me (at least, i manage to complete the "get 1 SR card" daili mission much faster if i click only the bottom middle one, than if i try to "catch" the SRs that sometimes spawn on the corners) and middle upper is almost always have an R card for me.