We managed to eat at both during our last stay (Tuesday before Thanksgiving through Wednesday after)
La Hacienda has a nice view, but I really like hearing the fireworks themselves. Yes, they pipe in the music and narration, but it's not the same (at least not for someone who LOVES fireworks like I do). It was not full the night we were there, so had no trouble moving to a table on the main level. You couldn't see the higher fireworks though.
Rose & Crown was VERY DISAPPOINTING for me this time. We had been 3 other times and enjoyed it immensely. We have been able to sit outside each and every time. But this time, we were put on the second level underneath some covering. We missed MOST of the fireworks! One couple let their child throw a fit so that they could be moved somewhere else. They must have known what the viewing actually was like.
Our last time this trip, we sat on the outcropping outside of Germany and LOVED IT! Even though Epcot felt busy that day, there were only 8 other people there besides my family of 4! Probably my best IllumiNations viewing ever and we've seen it A LOT! (Our 2005 visit I think we saw it most every night because the other parks all closed early! I definitely know we watched it a couple times from what used to be the outside seating at Mexico and 1 time Rose & Crown)