How to assemble a springform pan?
It's personal preference.

However, it's easier to cover the base of the pan in grease-proof paper when the lip is downward.  When the lip is upwards, it can be difficult to get the lining paper into the edges at the bottom without it crinkling a lot.

You get slightly less mix into the pan, but it's not really noticeable.  For me, it's easier to handle a downward lip.