Well, tax-deferred, since you don't pay tax until you sell. And if it's inherited, you get a free step-up in bases, so your kids won't pay the tax either.

And I think Kamala Harris really screwed the pooch on this one. She ranted about taxing unrealized capital gains, which is going to tick off pretty much all the billionaires (and therefore their monetary support would move to her opponent), whereas if she just said she'd tax stock grants for people in executive positions (or over a certain income), they probably wouldn't be as pissed because they're largely founders, and thus there's no stock grant to be taxed (it would mostly hit non-founder C-suites). In practice, this would just mean tax basis is stepped up at the time stocks vest, provided you're above a certain income.