I'd choose Biergarten over Teppan Edo, because it is different. We have a Japanese hibachi restaurant here at home. The food is the same at Teppan Edo, it just costs a lot more! Biergarten is FUN along with dinner. Even if you have a German restaurant near you, you more than likely don't have the whole German beer hall experience, complete with oomph-band and dancing! Also, although people worry about sitting with "strangers" at Biergarten, it's not bad at all. We have always found we have things in common with our table mates, and have enjoyed all our meals/experiences at Biergarten.
Our only "bad" table mate experience was at Teppan Edo. DD (I think she was 18 at the time) and I were seated with a family of 4 who probably should have done the afternoon nap thing (toddler slept in mom's lap, dad was short-tempered, 4 year old was cranky and threw food around) and a young couple who played tonsil-hockey throughout the meal. I wanted to tell them to get a room- and as we were all on the dining plan, I know that they had one nearby!