I originally posted this on math.stackexchange but was recommended to post here.
I have been admitted to two Master's Programs in math (both with funding). One is 1 year long and the other is 2 years long. I plan on obtaining a PhD directly afterwards.
The 1 year option lets me save one year. But I would have to apply to PhD programs within the first semester and it seems I would not have time to get good recommendation letters or make a strong impression from my Master's Program. The 2 years option would give me more chance to demonstrate what I've done.
If they are comparable programs, which would be the better choice?
I would normally choose the two-year program, for exactly the reasons that you cite. One of the few reasons why I would consider the one-year program is if there is a particular individual you want to work with, or if it is your first-choice school for the PhD program and it offers a path of lower resistance to already be a student there.
Otherwise, as JeffE points out, you won't really save much time by going to the one-year program over the two-year program. (Besides, if it's a coursework-based program, you'll probably get more out of the two-year deal!)