Biergaten is louder than San Angel. And as far as seating goes, unless you have a very large party, you will be paired up with others at Biergarten. But at San Angel, while you will have your own table, it will be so obnoxiously close to two or three other tables around you, it will feel like you have been paired up with others!
I don't give the nod, food-wise, to either place. I enjoy various types of wursts and sauerkraut, so I am always satisfied with Biergarten, but I certainly wouldn't rave about it. Sort of the converse of Pakey, I have had way too many good meals in Germany, Switzerland and Austria to be terribly impressed with Biergartedn, but I don't dislike it. San Angel is not your typical "Chili's" or "Chevy's" Mexican menu, but the dishes there seem to be on par with banquet or wedding food. Too mass-produced for my taste. But again, I don't dislike it. I just wish it were better.