You are in Y, so there is no significant difference (at least between LH and LX; I have no first hand experience with AC in Y). Some would try to avoid LX B773 flights which have 10 seats abreast in Y but the aircraft will be brand new. I like the IFE on the B773 and in general I prefer LX over LH. A transfer at ZRH is as less complicated than at MUC, so no significant difference there.
No first hand experience with AC in Y, but to transfer and clear US immigration at YUL is quite easy and quick. And no need to clear immigration at LAX afterwards. However, I wouldn't be in favour of taking a (a rather long) shorthaul flight after the TATL longhaul flight - I prefer it the other way around.
Just a take a decision - which carrier you choose is not going to make a significant impact on your travel experience (at stated above you are in Y so you need to get it over with as quickly as possible)
Last edited by SK AAR; Oct 11, 2017 at 5:02 am