Jaymarshack,in keeping with your exact question,please allow me to chime in.I have heard both speakers quite a few times,with different components.Both analog and digital,so I have a fairly good impression of both.The Alto is the newer design,with the Utopia as the more vintage design,but NO slouch!!
I have NO JM Labs stuff,yet have always been fascinated by these products.What got me interested was going to a dealer,to hear an Avalon Eidolon,and being able to A/B the original Utopia with it.I was shocked,as to how much more real sounding the Utopia was,as opposed to the rather "thin",in comparison,Eidolon.Yet the Eidolon is still a superb design,and worthy of it's reputation.
That was the beginning of my admiration of the JM Labs "big boys"(Utopia line-up).I have heard even the Mini Monitors,which are real giant killers,IMO.BTW-this is all only my opinion,yet the products are superbly made,fairly easy to drive,and are convincing music reproducers.
To be specific,the Altos are a wonderful design,and can fill a fairly large room,with a good,yet modestly powered amp.Truthfully I believe the Berillium tweeter is very good,yet the marketing campaign is overstating it's significance.It is very good,but many of the better tweeters(from silk dome to other types)will sound just fine if the designer voices his product properly.It's about getting a good balance,with good harmonics,and timbres.All in a full range sounding design,that does not pose too high a demand on the amp.
The Alto will probably keep anyone quite happy,unless the room is huge,or you are bass obsessed.It does not have the best "mid bass" definition,but that's nit picking.A nice design,and a beautiful looking box.I like it.
The UTOPIA(not the Nova,though I have heard it a few times)I have heard on loads of occassions,and am absolutely convinced that it was/is a "CLASSIC"!I actually had the pleasure of hearing it at Jonathan Skull's home,some time ago.He was the reviewer for Stereophile.I thought he got good sound,from it,but at the time he demoed it for me,he was using a 100 wpc Cary stereo amp.It sounded very dynamic and warm(in a good way),with room filling sound.Very nice.However it had a midbass hump,that I attributed to the amp.Not enough control of the woofer.Large room,and it was very far out into that room,btw.Great, high ceilings,too.
I heard this speaker driven with every type of amp,and the best I ever heard it,by far,was with a 200 wpc Yves Bernard Andre unit.On two occassions.In different systems and rooms.The first time was with a superb VAC tube line/phonostage,driving the YBA solid state amp.The second time with all YBA stuff.I suspect the amp must be of paramount importance,in controlling that woof!I know Jonathan Skull preferred solid state,here.REALLY good solid state.As in "pricey",but WOW!BTW,I like both tubes,and solid state.It is the speaker/room that tells me which sounds best.The Utopia needs woofer control,and there are good tube choices too.The newer VTL stuff,as one example.
On the first occassion, where it sounded great,I brought my own LP's and CD's for reference.The sound was stunning.Really "real" sounding.Gorgeous tonality,and perfect midbass/bass,with no bloat or colorations.The speakers were closer to the back wall than at all other times,which probably gave a better solidity in balance.Room related,I guess.I LOVE this speaker,and if you find a nicely kept pair,in good condition,you will be in love too.
The Nova is a highly rated speaker,but(only my opinion,remember)it suffers from way too much marketing hype of the Be tweeter.It is not as good sounding a speaker as the original Utopia,IMO.It is lighter(cabinet weight)and more agressive sounding.Dynamic,detailed and NOT as Gorgeous sounding as the Utopia.Music is gorgeous.It should be conveyed as such.The Utopia will still sound gorgeous(assuming you feed it good equipment,and a good room)ten years from now.Not coloration "gorgeous",but musical gorgeous!You know what I mean,if you are a music lover,first!
I ran into Mr. Skull(a nice guy,btw)at a recent audio event,and reminded him that I had heard his Utopia system some time ago.I asked if he still had the Utopias,as he is an equipment lover,and he may have gotten newer stuff.He claimed that he felt the Utopia was superior(in his opinion)to the Nova,and still owned/loved his pair.I agree!!
Hope this helps you,and it is all true!
Best of luck!