Well, I firmly believe it all boils down to what you want out of a character breakfast. Both restaurants should be able to accommodate your boyfriend's allergy so I would not worry so much about that, but Goofy's and Minnie's are very different.
Goofy's has a wide selection of items to choose from. Both traditional breakfast and some very unconventional items. The food is good, but the price is steep. I usually pay about 30+ for a "brunch" at Goofy's. I do enjoy being able to get an early PS before the park opens and have breakfast and be at the park for rope drop though. It is a wonderful way to start the day. The one downside for Goofy's is the fact that there seems to be a lack of characters. I always see Goofy, Pluto, CHip and Dale and Baloo. On my last trip I also saw Jasmine and Alice. This was the most characters I have ever experianced at Goofy's though. Many other DISers share the same feelings regarding this manner. Simply put... for the amount of money that you pay, GOOFY'S NEEDS MORE CHARACTERS!
Minnie and Friend's on the other hand has an abundance of characters. On my trip there on my last trip we saw Rabbit, Pooh, Tigger, Max, Captain Hook, Chip and Dale, Fairy Godmother, Minnie and others that I can't remember. The food was good, but it is only standard breakfast fare. Breakfast meats, waffles, eggs, potatoes, biscuits and gravy, cereal, pastries and muffins. Goofy's has all of the exact same items and more! Due to the lack of variety the bill is smaller at a more reasonable 23ish dollars. So Minnie and Friends gets points for the price. Lastly, you can not beat the location for minnies. You are sitting on main street eating a good meal surrounded by Disney Characters. Makes for some good memories and photo opps.
Like I said, it all really depends on what you want out of a character breakfast. Good luck
