I agree with Raid's recommendation and order but would add a 90/4 Leica. A small lens, reasonably easy to find and does sharpen up at 5.6/8. I had a M mount for my carry everywhere kit for years and loved it.
I have a 105mm Brightline finder for sale, my reserve was $200 and it never met it on EvilBay. I will be putting it up again soon. I have two 105 for RFs, one for my S3-2000, the other for my M4-P (I also have it in F mount). The lens is the best portrait lens ever made and not impossible to come by. I paid over $300 for the finder two years ago and love it. I'm selling it because I'm between jobs and I do not need one for the S3-2000. On the M4-P I use the 90 frame lines and tighten up a bit.
The Steinheil Munchin is said the be a great lens, I never got one for LTM. I got a Exacta one by accident and turned it. Everyone who has had one loves them.
If you are looking to carry the lens all day around your neck, Steinheil or 90/4 Leica. If you use it from time to time, the 105/2.5 is the way to go. Also, the 105/2.5 takes 52mm filters! This means you can get a hood for it and also TONS of Nikon filters fit her (e.g. Soft-1, L-37, ND-400) which you can not say about the 85/2 (she has a older pitch to the threads).
B2 (;->