Loake 1880, Meermin etc and below=everyone use plastic heel- and toe stiffeners. In the mid price range with brands like C&J, Carmina, Church's and so on it's also very common, just in some cases that they use leather heel stiffener, still plastic for the toe though. Actually, even the finest RTW brands like Edward Green use plastic toe stiffeners as well, but leather for the heel (since the possibility to adjust shape better to the foot is more important there, one tend to take the extra cost of using leather at least there). But for example John Lobb Paris use plastic both for heel- and toe stiffener.
Meermin Linea Maestro line uses pre-conformed leather heel counters and for the toe stiffeners they use glued fabric placed when lasting and formed when dry.
Mostly everyone uses heat formed (celestica?) toe stiffeners for mass manufacturing.