For regex specifically, the usual "regex" crate is fantastic and provides very good performance guarantees (no exponential behaviour, ever!), unlike a lot of regex libraries. However, it also comes with the tradeoff of not supporting arbitrary lookahead/lookbehind or many regex extensions, so people needing those features might need a different crate.
There's a nice discussion on another thread: https://news.ycombinator.com/item?id=33510976