If there's heavy trashing of coppers, you probably want at most one stable for the early mid game, and then go labs. However, even discarding a silver to stables is sometimes preferable to playing a lab. Having labs make your stables more robust to low treasure density.
Obviously though stables is better without copper trashing. I'd buy ~4 stables first, then I guess I'd switch to labs, but the game probably won't last that long. I think you'd be ok buying only stables. If all your coppers are around, it's relatively rare to never get one.
In cursing games, the calculus changes a little bit. You still probably want stables first, but I think you could run into trouble if you went all out on the stables. I'd probably get 2-3 then start alternating between lab and stables.
With discard attacks, again go a little less heavy on the stables, but still probably get at least 2 or 3 then alternate.
Overall, without trashing stables is significantly stronger than lab.