From the whiteside, I think there are many ways to handle the stonewall. The easiest of which is at one point or another play b3 and Ba3 (prepare it if needed) and trade your bad bishop for their good.
The leningrad looks crazy to me, but seems playable... it lacks a plan I think. It's a classical but with your bishop on g7, so if you ever go for a kingside attack you spend more tempi on g pawn and bishop moving.
I am planning to develop my knowledge of the Dutch Defence and I find that GM Simon Williams has recommended the Classical Variation, which to me does not seem too fun. I was wondering what you thought was the best variation?
I currently favour the Stonewall to the Classical, and I rarely play the Leningrad because it seems too risky to the King.