I played both pieces today side by side. Overall they are pretty similar. They're very close in terms of brightness/darkness with maybe the A28 being a tad brighter. I thought that the A28 was easier to blow and that it had a little clearer sound. But the A27 was more complex and more depth of tone, and thus more harmonically rich which isn't what I was expecting based on my memory of the 2 pieces. Like I said, they're pretty similar but if given the choice, I'd choose the A27.
FWIW, I was play testing them with Rico Reserve 3.0+ reeds and a Rovner Mark III Ligature on a Yani 880.