What stop-limit do ya'll typically use?

Tons of variables on this imo....what is the holding compared to you portfolio? What is the holding compared to the specific sector overall? What's your age and pain threshold? You can't just blanket a 10% stop loss rule of thumb on stocks...especially for volatile positions. I would look at a lot of things but one in particular is "at what price would I have not bought this stock". You have to take as much emotion as possible out. If it's a volatile stock in a sector that all indications should do well in the current conditions, and you really like that specific etf/company then you could look to buy more at the lower prices instead of getting out...obviously that's dependant on a lot. you could just protect the position with a put option..ladder it if need be.
When is the juice not worth the squeeze to you? That's you stop loss.

Stop limits at opening bell are hugely dangerous especially on securities where mm's control the spread. The real inside, not the hidden inside, which isn't always easy to determine. You would be better off using some sort of hidden order, but only after checking level two, and attempting to route the trade for more security. Route it directly to someone who has a large block at the ask.

If you trade/invest on IB, I'd route it to a dark pool. Or tow a platform that rebates commission. A liquidity adder.