I haven't heard the Alons, but I spent plenty of time with both the Fidelios and the Merlins so I know what they are capable of. Both speakers are exceptional and if your room is not very large, you would be hard pressed to find anything better at any price.
There is a lot of similarities between these speakers: they are priced similarly (although the price on Verity products has gone up quite a bit lately), their designers really know what they're doing and are willing to patiently guide you with the setup and choice of electronics, and most of all, these speakers sound pretty similar too.
They both offer a very natural and transparent sound with great soundstaging, bass and dynamics that belie their relatively compact size and superb refinement across the spectrum. Both are easy to drive and pair well with tube amps. The differences are subtle and the final choice would depend on your taste as well as the matching electronics.
I personally prefer the Fidelios. They came out as a little more involving and musical, a little more polite, especially in the upper midrange that sounds smoother, richer and more liquid than the Merlins. I found that the Merlins can at times sound a little overenthusiastic, making some recordings too bright and dry. The midrange is excellent in both cases, perhaps with the Fidelios possessing more of the "see through" quality that demonstrates itself in a natural and lifelike presentation of vocals and acoustic instruments. The treble is well extended, smooth and refined in both cases and the bass can hit surprisingly low too. The Fidelios seem to image a little better and the soundstage depth they produce is spectacular.
Go for the Merlins if you prefer a little brighter and livelier presentation and choose the Fidelios if you want something just a touch more smoother and richer.
