Absorbing damage with Planeswalker
Neither. Treat your planeswalker as if they are a separate player, one that you can use your creatures to block for. If there is trample damage when your block, that damage goes to your planeswalker, not you. If you don't block (or do block and there's trample) and that damage is more than enough to kill your planeswalker, then your planeswalker dies, and no damage is dealt to you. Damage never tramples over onto you from an attack at your planeswalker. From the comprehensive rules (emphasis mine):


  510.1b An unblocked creature assigns its combat damage to the player or planeswalker it's attacking. If it isn't currently attacking anything (if, for example, it was attacking a planeswalker that has left the battlefield), it assigns no combat damage.