I enjoy BOTH about equally. As Christmas is my favorite holiday and Winter is my favorite season, I love Winter Summerland - especially the Winter course! Like Blizzard Beach itself, it's a brilliant concept to bring a little Wintertime magic to the typically swelteringly hot Florida!
But as a HUGE fan of Disney Animation, I ALSO love Fantasia Gardens. It really captures the charm, whimsy, and music of some of the segments from the classic film, Fantasia.
I find them both to be really cute, whimsical, and have great music! So I try to do all three courses (Winter, Summer, and Gardens) about equally.
I wouldn't recommend the Fairways course at Fantasia Gardens unless you are a REALLY good golfer, though. It's MUCH more difficult than a typical mini golf course, and it doesn't have the cute touches like the other 3 courses have. It is really geared more for the serious golfer than the others.
For what it's worth, I don't find the regular course at Fantasia Gardens any more difficult than Winter Summerland - it's the Fairways course that is really hard.