What are some of the most underrated and overrated loudspeakers you’ve auditioned?

The ADS L620 is my choice for the most underrated loudspeaker. I've seen comments regarding the combination of a 10 inch woofer to a 1 inch dome tweeter as a bad marriage because the mid range suffers. I say bull****. I've owned a pair of these loudspeakers for many years and I can say without a doubt they will best many new loudspeakers currently for sale today for excellent sound quality and clean tight bass.

Overrated: Bose

Underrated at the price: Magnepan MMG

Notes: Never heard a Bose speaker I liked....MMG's require clean amplification (clean, not exotically elegant) and a subwoofer.

One of the most overrated speakers IMO is the Pioneer SP-FS52 floor standers. The tweeter supplied with this speaker was of poor quality and it failed rather quickly when driven by an Acurus A200 amp and B&K PT3 preamp at far below rated input power. I replaced the substandard OEM unit with a Peerless replacement and these speakers sound so much better. In their as manufactured state they just don't deliver the goods as well as the reviews state. 

mahgister

You do realize that the MMGs are Magnepan's entry level speaker and cost $600/pair, don't you? You called them "top level speakers" and then proceeded to discredit them when compared to your Mission Cyrus 781 at $900/pair. Sure, the MMG owner may not have prepared his listening room correctly or even had them set up correctly, negatively impacting the sound, but Magnepans have traditionally been thought of as some of the best value speakers on the market, regardless of price, especially when paired with a sub. It's possible that I'm a bit biased because I bought a pair of 15 year old Magnepan 20.1s (originally $12,500) for $5,500 and absolutely love them, but I think the only speakers that can compare to them cost more than $20,000. This is the price point at which we begin talking about "top level speakers".

Overrated; Martin Logan  Electromotion ESL, on a demo they hooted and buzzed at me, and got real confused. Partner with me said exactly the same. Following this demo immediately with Focal Electra 1038 Be which were several leagues above the ML, and I bought them. Not that I dislike electrostatic sound having owned Quad ESL 63's for 10 years and Cadence Aristas for a further 10, but the sound produced at demo by the ML's was really below expectations. Could have been the rest of the gear, but in common with most hi-fi demos they surround the gear you are interested in with top end kit.