A slower one. A calmer one. A more serene and balanced and outward-looking one. One in which the pressures of survival in a biologically unavoidably finite sentience don't compel one to make decisions based on "balancing" long and short term.
I'd still do unto others as I would have them do unto me - only now, not just for reasons of "right and wrong" (and eternal self-preservation in an attempt to please God), but because if we're immortal, then time guarantees that what I give and do to and for the world, would surely eventually be done back unto me.
I'd take active and time-consuming (endless supply, right?) care of the natural world and pay attention to sustaining IT, not depleting it for selfish or self-centered purposes, in a meager attempt to achieve an equal symbiosis for that which is supporting and sustaining me so well.
I'd still regard children as God's blessings to the world (even though, in this immortal scenario - adding generations to a population that doesn't die would have to "magically" defy karmic and Newtonian law. Matter would have to be created if nothing "died".
And - hey, now this is a cool thought-thread - wars would be futile! We'd actually have to figure out how to SOLVE problems, not just fight them until the "stronger" or better-resourced fighting unit "wins".