Level 1. It takes less time to repair, cheaper and does the same job as Level 2. Armour Plating is great with Level 1. I’m not a fan of using Fort HP either, because when destroyed, you just take even longer to repair. You can get more stuff done and more productive, if stay with Level 1’s.
A Level 2 Barrier is worth two Level 1 Barriers. You’ll be way more productive to build many Level 1’s, right off the bat than doing Level 2’s. Level 2’s seem like a waste, especially before Lockers or whole base setup. And two Level 1’s cover more area, compared to a single Level 2,
When playing as Jack or bought a Repair Tool, it’s faster and cheaper to do Level 1’s and longer, more expensive to do Level 2’s. Sometimes, the two ends of Level 2 Barriers can block line of sight, so you end up hitting the Barrier. It wouldn’t be an issue with Level 1’s.