I choosed B system when I switched from PA.
I switched because my first accordion teacher recommended. He told me "professionals play CBA and you should too" it was back when I was on second grade in childrens music school, of course I wasn't professional
CBA was and is still quite rare in estonia due to political and ideologic reasons, but before WWII there were many CBA players in estonia. So in soviet time and after it was only for those who didn't care about politics or studied in some european or russian conservatory. I wasn't able to buy CBA until I finished childrens music school due to low budget. My first accordion teacher passed away when I was in third grade and after that my second teacher wasn't interested at all from switching to CBA. Actually my first teacher started with CBA when he was young but switched to PA because there wasn't any CBA teacher in estonia after war. We planned to learn B system because it was main system in Russian and used Weltmeister and Royal Standard CBA's were readily available. So my first CBA was Royal Standard Romance B-system CBA. I am quite happy actually that I choosed B system. Since I learned CBA myself I considered switching to C system from B because I like triple voice musette and french musette instruments are mostly C, thankfully I discovered dutch accordion players and fact that they used mostly B system
so my day was saved and no switching needed, some time later I bought used CBA from netherlands.
I think that both systems are completely equal because they are just mirrored. It is very unlikely that there are compositions that are playable only on one system.
I don't avoid using thumb, I use it always when I need
I think there are mainly two types of technique - four finger and five finger - both are used in both systems, difference is only which one is used mostly due to systems mirrored nature. There is actually couple books published for five finger technique for B system - sorry no english version available
А. Полетаев - Пятипальцевая аппликатура на баяне - http://ale07.ru/music/notes/song/bayan/applikatura5.htm
Ю. Бардин - Обучение игре на баяне по пятипальцевой аппликатуре - http://ale07.ru/music/notes/song/bayan/obuchenie_5a.htm
They are downloadable, click on "Скачать".
I don't know but I suppose that there is a lot more virtuoso, analytical, technical and pedagogic repertoire material available for B system. Correct me if I'm wrong
Russian bajan masters have published a lot in the past and still do. Always when I try to search etudes or other tecnical material for C system I almost don't get anything, but for B systems there is whole library from material for beginners to conservatory level. Probably many of us know F.Lips - Art of Playng Bajan, there is actually many similar books - http://ale07.ru/music/notes/song/bayan/posobia.htm
Etudes for childrens music school, book for every grade and every book consist of sections devited for different technique, These are very practical for beginners! - http://ale07.ru/music/notes/song/bayan/ ... ehnika.htm
Lot of general etude books - http://ale07.ru/music/notes/song/bayan/etudy.htm
Beginner tutor books(there are also russian PA tutors), pedagogic, technical and other(old and downloadable ones) - http://ale07.ru/music/notes/song/bayan/sam_bayan.htm
Virtuoso compositions - http://ale07.ru/music/notes/song/bayan/antologia.htm
And so on.
These are old materials, there are russian book shops that sell also new books.
I recommend to look around further on ale07 site, I don't know exact russian copyright laws but seems that they honor them because they publish only old and possibly out of print books - http://ale07.ru/index.html
If anybody is brave enough to look into some of these books beaware that there are two type fingering marking system.
1)Fingers are marked from 1-4 and thumb is marked with russian letter "б" it is used when four finger technique is mainly used.
2)Fingers are marked from 1-5, this one is probably mostly used in newer books.
I prefer second type, it is not so confusing if one don't speak russian. I remember my horrible mistake with first type when I started with CBA, remember if you see "1" try to figure out is it really thumb or just index finger!