I use both of these amps.
In "general"....I like the very top end of the 2a3 best. I like the 300b midrange better. If I could only have one, it would be a really good 300b.
They will sound more alike than different when compared to transistors, digital amps, even other tubes like tetrodes and pentodes.
With your speakers, I don't think you would go wrong with either of them. I do doubt that the 2a3 you are looking at puts out 8 watts "if" it is truly single ended. Usually it's around 3.5 or 4 watts. As Charles mentioned, it might be a different circuit other than SE but with your AN's 98 db spec and your listening tastes, it may be moot. The difference between 4 and 8 watts is only 3 db.
My guess is you will like both but will prefer the 300b.