Having eaten both, I'd eat both. Sadly, the Grand Mart that stocked these doesn't anymore (they were reasonably overpriced for what's essentially only as filling as a snack at $2.50 a bowl).
The Kitsune Udon (red) bowl is good. Very good even. However, unless you let it sit in the broth for a bit, the aburaage is a little TOO sweet. Delicious when just right however (if you're careful with it; if you bite too much, having soaked up all the hot broth, the aburaage sheet will burn you painfully).
The Tanuki Udon flavor is great. The tempura/wafer/cookie/thingy is delicious. The slight problem it has is that the damn thing is essentially no so much tempura as a dried-out funnel cake with shrimp and seasonings on it. That itself isn't so much the problem; the main problem is that the damn thing soaks up broth too damn fast, and breaks apart from being too soggy. However, I find it the more fulfilling of the two flavors.