I mean, Dems definitely gerrymander also, but they're neither as shameless nor as sophisticated. And certainly the republicans have more options (states), but the tech they've employed (redrawing software like Maptitude, although I bet dems used it too) is better, the campaign strategies they ran in advance with their eyes on gerrymandering were dirtier (operation REDMAP in 2010), and the financing of their efforts is stronger (thanks, Citizens United).

I could be wrong, but California and Pennsylvania also seem like bad examples, since California has had a redistricting commission since the Governator and PA just had their Supreme Court overrule Republican gerrymanders last year. Those states seem to lean blue now off social geographic sorting.

Dems have done some dirty politics gerrymanders; Repubs are on some espionage-level shit with it.