I have a pair Bose A20's and the original Zulu's and I think the biggest factor is which one fits your head better.
Before building my RV, I was a bit of an audiophile I really did not want to buy anything from Bose, as any of their speakers, etc. that I have looked at appeared very overpriced for what you were getting.
However, the A20's fit my head much better than the Zulu's did........
At the end of the day, I'd try and find a pair of each to try on and buy which ever one fits/seals better.
Jason