The shape will have an effect, but I think the compression is a bigger factor (and the storage environment, of course). Most tuocha and bricks are more tightly compressed than most cakes, and tend to be made with lower quality raw material, but there are plenty of exceptions to all of these.
Also depends if the tea has had traditional storage before you got it, and what kind of taste you prefer.
As far as your super tight Xiaguan tuocha, I don't want it unless it had some pretty wet storage early in its life.
I would avoid the melon shapes altogether, and especially so if you live in a dry climate.