Which energy drink brand won't destroy my teeth?

Energy drinks are all acidic, full stop. Low pH is what actually ruins your tooth enamel, regardless of the brand. That said, some are less bad than others - sugar-free versions have less sugar which at least doesn't feed bacteria, but the acidity is still there no matter what.

If you absolutely have to drink them, look for brands that already focus on less aggressive formulas, like ones with xylitol or that add calcium. But honestly the real trick is not keeping them in your mouth like it's a sip of water - drink it all at once and rinse your mouth after, don't sip it for hours. And if you can, wait a bit before brushing your teeth because when the enamel is already attacked by acid, the toothbrush just makes things worse.

The reality is that no brand damages your teeth less than the others if you're drinking them regularly. If you really want to protect your teeth, go see your dentist and ask them which brands are at least not the absolute worst in their experience - they see the actual damage every day.