Hi, i bought a m8.2 last month;upgraded from an x1 i liked very much. It is really up to your preference whether you like 28 (equals 36mm) or 35 (equals 46mm). For myself, i found myself cropping a lot of pictures taken with the x1 and decided for a 35 cron asph on the m8.2. Perfect for me and the lens is incredible.
Also to consider is a new 35summarit, a new breed of leica lens that is just very good as well maybe at a same price as an old cron.
Further, i am new to rangefinders and find that there are more things to consider. A bigger lens will block part of the viewfinder, something i wouldn't want. Longer focal length use only the middle part of the finder and are more difficult to frame and focus. 24mm lens will use all of the viewfinder to frame, 28 and 35 are perfect in my opinion, 50 is ok. But chrck it out yourself.
Good thing is to try the exact lens you want to buy on your m8 body and check if it focus correct (full open, stopped down, close distance and infinity). In this case you will avoid dissapointment when you find the lens (second hand) is not correct adjusted.
Anyway, the m8 is incredible, you will love it.
H