What is the safest ppi to take long-term?

Same in general. Drugs in the same family don't always work as expected in all people so your doctor would have to find the one that works best for you. They also share the same side effects so talk to your doctor about the side effects and complications so they can be monitored such as success of treatment, your magnesium level and the integrity of your mucosa to avoid effacement or atrophy.