I've done both, and prefer "Winter Summerland" (Blizzard) over Fantasia.
A few notes about how your WP&M credits work that I learned on this last trip...you can use them any day at any venue, but only ONCE per day for said venue.
In other words, if you do the Winter Course at Winter/Summerland, and then want to do the Summer Course, you will either have to wait for another day, or pay. However, they did honor the "second round" price for me and my kid when we did it, and it cost 12 bucks for both of us combined, iirc.
The Summer Course, I think, is the better of the two, mostly due to the closing holes. The rest of the holes are themed differently, but pretty much replicas of each other.
Hope this helps!