I would go with the Monitor Audio i-Deck. Despite them being discontinued they are still probably the best 2.0 computer speakers for under $300. They are better than the AV40 IMO. I've owned both. The constant humming and exaggerated bass on the AV40 were too much for me to put up with. No such problems with the i-Deck.
I haven't owned the Audioengine A5, but in a review on Macworld they gave the i-Deck the same rating as those ones while also noting that the i-Deck had better treble detail. I've never owned a speaker with better highs than the i-Deck, although i think the bass on the A5 will go deeper than both the i-Deck and the AV40.
I paid £30 in the UK for a used pair in good condition. Compare that with what they are charging for the AV40 and A5 and the choice suddenly becomes clear.