I used to use the spear mostly, but recently started using lance. Sword (lv9) is also pretty good, depends on your gameplay. I tried to use the maul but didn't have much luck, but I still think it is a good weapon if used correctly.
it does give you phys immunity however grapples and some world weapons arent affected by this and will still damage you. You're better off using something else for your relic unless you can constistently chain kills otherwise you really wont gain the full benefit of this relic per game