Had a look and listen to a few affordable speakers today and thought it might be useful to share my brief observations for each one. Heard them all on the end of a Denon PMA720AE amp as this is what I am familiar with.
Monitor Audio BX2 - Wide, spacious sound with lots of detail but lacking body overall. As I experienced when I owned a pair, they tend towards being a bit soul-less and I don't feel I want to carry on listening for any extended period. Beautifully made. £249. 4 out of 5.
Wharfedale Diamond 121 - Full, slightly warm sound with more presence and body than the BX2s. Narrower sound-stage but more keenly focused and with very good detail levels. Really nice sounding speakers, completely let down by fit and finish. The black vinyl surface is cheap looking as is the black plastic front panel, and the vinyl covering didn't meet properly at corners. I've long had concerns about Wharfedale's finish quality, being the owner of Diamond 9.1s and Diamond 10.3s, and things don't seem to be improving at all. Not really acceptable when other brands can get it right. £229. 4 out of 5. (If they could get the finish sorted, 5 out of 5)
Dali Zensor 1 - I've owned a pair of these and, as then, today I found them to be very communicative and detailed if slightly lacking in warmth. They control the soundstage well and are both explicit and refinded in the treble. Nicely finished too. £199. 4 out of 5.
Q Acoustics 2020i - Small but deep cabinets, pleasant looking but fairly unassuming, though nicely finished for the asking price. Warmer than the Zensor 1s and BX2s but more open sounding than the Wharfedales. Really immsersive and involving to listen to with a huge amount of detail nicely presented rather than thrown forward. Have the special quality of making you want to carry on listening. Impressive little speakers. 5 out of 5.
To sum up, all four are very talented speakers and each could make a great buy if partnered with the right amp. The biggest disappointment is the finish on the Diamond 121. They are clearly superb speakers but even at this end of the market it should be possible to make them look and feel better. In terms of sound per pound, it is the Q 2020i which take the crown for me - super speakers, performing beyond their price.