A stonelord paladin is in serious danger of having no effect on the course of battle; they give up smite evil for an advantage when sundering, which will only occasionally be useful. So they're almost obliged to go for an offensive weapon - which means a two handed weapon, maybe a reach weapon so they can sunder without having to spend feats on such a specialised tactic. If you get a tower shield there is no good reason for monsters not to ignore you while they deal with the real threats.
For feats - power attack, of course. I'm guessing you want to be a tank so Steel Soul to make up for the lost Mercies. For the other two, if you have dex 12+ Combat Reflexes is useful to a tank and Furious Focus will always be handy with Power Attack. Lunge is also useful.
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Stonestrike isn't just about sunder, it's also freaking awesome for fighting robots and animatied objects. Creatures with hardness are a serious pain and the stonelord is one of the few classes that can deal with it without an adamantine weapon.
That said, I will second a big reach weapon. I'd recommend the Dwarven Longhammer or Longaxe. They are martial weapons for you, counteract your lack of mobility in a defensive stance, and back a whallop. The Lucurne Hammer is also good, with decent abilites, multiple damage types, and a big die.
Also, get a dwarven boulder helmet as a secondary weapon. You will threaten both reach and adjacent.