Recommended snowboarding resorts from Zurich

I will be flying into Zurich and have three days to spare. From looking at the Lonely Planet I found three recommended resorts- Engelberg in Central Swiss, maybe near Zurich and then Davos-Klosters and St Moritz both in Graubauden. Which should I go to, or are there any better places? What is the best way to get there?

As a boarder who lives in Zurich, I would recommend Flims/Laax. Big, lots variety, has a glacier and even on busy days you can find a quiet piste, some nice off Piste opportunities was well.
I prefer it over Davos. St Moritz is really expensive.
From the Airport it takes about 2:10 hrs to get there. Take a train to Chur and then the bus from the train station to Flims/Laax.

Is the snow quality better there?

Sounds cool. Not so worried about the costs, will stay in hostels anyway, as it is a short trip just want a good experience. St Moritz is really famous though, right.

Snow quality doesn't vary to much between Flims and Davos ( both in Graubunden and not far from each other). The snow on the Glacier at Flims is always excellent and also around La Siala.
What I prefer about Flims is I can get anywhere by lift/boarding, everything is connected , whereas to get from one area of Davos to the other involves taking a bus/train.
Also there is less walking/flat bits for a boarder on the Flims pistes compared to Davos.
Yes, St Moritz is famous, never been there myself.