My first Leica (and only one) was/is a Barnack, and I like it a lot: a IIIF. I use three lenses on it: a CV 28 3.5 (I had it before getting the IIIF), a KMZ I-50 (collapsible, the one I got for it first) and a KMZ J-3 optimized for close focus/wide open shooting (very light and fast, the second one I got for it). These two 50's give the old, classic look to photographs, being lens designs used for nearly a century... I guess both are identical to Zeiss lenses, and perhaps used German glass, German technicians and German machinery, apart from German design...
This camera made me feel the Leica feeling: a feeling about cameras, not about lenses IMO... My M feeling is named Bessa R4M & R3A & T... When I've used M Leicas, I haven't felt them as Leica as my Barnack, but closer to my Bessas... I might add M Leicas to my cameras someday, but to me Leica gear is secondary, as I can do with my Bessas everything Leicas can do, but Leicas can't do everything my Bessas can do...
When I wonder which Leica will be my first M, I use to think it will be an M2.
Cheers,
Juan