I own a pair of Marten Coltrane Altos, so I know from whence I speak. Firstly compared to the Miles 3, the Coltrane Altos are in another class. The Miles 3 is only the middle speaker in the Heritage line, whilst the Coltrane Alto was the entry level into the Coltrane line & featured the finest Accuton drivers, Jorma No1 internal wiring, ultra high grade crossover & a carbon/kevlar monocoque cabinet which 'disappears'.
The Avalon Indra is a $20k speaker & is very good, but lacks bi-wire connections. The Coltrane Alto listed for $24k 6 years ago. The Altos are more extended in the top end than the Indras, and because of the extreme quality of its components and design, I would expect the Altos to be a more refined and accurate speaker overall, and for me, ultimately a more satisfying speaker. In the end however, it comes down to personal preferences and taste. The Indras would be best suited to a medium size listening room.
If you're going to be doing mostly low level listening, I would have an audition of the Wilsons, and the Altos (if you can manage to locate a pair (virtually unobtanium!))