Xidi is nice; it's not overly commercialized, and you can see the villagers' lives. It's rustic and steeped in history. The village is well-preserved, perfect for a leisurely experience. However, wandering around on the off-main roads after dark can be a little scary. There are folk performances in the square at night, which are very lively, and at 11 pm, they even play gongs and drums to signal the night watch.
Hongcun is heavily commercialized, with assembly-line-like shops selling cultural and creative products, Hanfu (traditional Han clothing), silver jewelry, and even grilled sausages—it's pretty much the same everywhere in China. But the morning and night views of Moon Pond and South Lake are worth seeing.