Absolutely La Hacienda! After several visits to San Angel over time, we were excited to try La Hacienda earlier this year. We love it!
1) Atmosphere: La Hacienda is right on the lake, with a beautiful view out of the amazing large windows. Some tables are in the back a bit, so you might want to request a table near the window in the main dining room. During our most recent visit, our table was not next to the window, but the view was wonderful anyway. Of course, it's relatively new and that shows - high ceilings, lively atmosphere, great decor - just very well done. I bet it's amazing during Illuminations - our ADR was around 6:30pm, so we didn't stay long enough to see it from the restaurant. While San Angel is fun because it's right on the edge of the Three Caballeros ride river, there are few tables actually right on the river.
2) Service: Service at La Hacienda was friendly and efficient. We were seated very quickly - just moments after our ADR - and CMs were particularly upbeat.
3) Food: No question, our family prefers La Hacienda. We're a family of five and we all have very different tastes, but everyone enjoyed La Hacienda. The menu is interesting enough for our more adventurous eaters, but still has some standard children's items for our pickiest eater. They modified some menu items for our oldest - who wanted a smaller portion, but something more than plain tacos. I should add that both my husband and both of his parents are Mexican, so we cook and eat quite a bit of Mexican food at home - and La Hacienda is one of our favorites at WDW!