We have eaten at both places and have enjoyed both. They are both so different though so it really depends on how you look at it. You should weight out your options. Here are our pros for both places!
Garden Grill - Characters are awesome there, Chip & Dale are very very funny and who doesn't love Mickey and Pluto! Plus the restaurant is in the Land pavilion so very very close to Soarin which is a plus if you can coordinate your FP or a down time for Soarin with your ADR. The food there is pretty good and its brought right to your table and if you want seconds of something you just need to ask for it no problem, so its like a buffet that you never have to leave the table for, lol. The restaurant also rotates slowly so you get to see a portion or that boat ride below it which is cool. The wait staff has always been friendly there when we have went as well. We love Garden Grill and its always a must do for us when we go to Disney. We are excited to try their breakfast though this time around!
Teppen Edo - This is a typical hibachi type restaurant, the only problem I have with this place and I tell everyone that if you have a decent hibachi type place near you that you have been to, don't compare the 2. Teppen Edo is what I like to call "disneyfied" hibachi, lol. Once you have realized that though this place is a TON of fun and the food is actually really good. We went here in 2014 for the first time and my older son (he was 7 at the time) was actually quite disappointed bc the show wasn't what he was use to. We have a lot of hibachi places near us so he has been to a good amount of hibachi grills. Anyways he kept asking me where all the tricks were, but the chef told him he wasn't allowed to do them bc this was Disney. He was disappointed, but then he ate the food and like I said we thought the food was really good! It was so good that when we went back to disney in 2015, my older son (now 8) asked to go back to Teppen Edo. He didn't even care about the hibachi show he just loved the food.
Both places are really good and we like them both. You won't be disappointed with whichever choice you make though. They are both fun places to go!