I did not want to make a case for vintage machines, but I guess that I must 'fess up to my stable of band saws. My main user is my 20" Delta. I run a 3/8 blade and pretty much only cut bowl blanks and rough straight grain blanks. If I want really accurate rip cuts, I switch to a blade that has not done circle cuts. I also have my 19teens Crescent 20", but that only has 7" of clearance below the guides. I will use this mostly for scroll work and keep a 1/4" blade on it. For really heavy work, I have my 36" Jones Superior. This saw has a 1" blade and does not get used for any kind of scroll work, but it sure is fun to use when you use it!
The important thing, in my mind, is that the saw fit your needs and budget. A 36" saw will be big and heavy. On my Jones, I can barely lift the auxiliary table. The main table is about 30'x30" worth of cast iron and is not to be trifled with. On the other hand, the table on my 20" Delta can be manhandled by one old guy like me, if necessary. Yet that table is more than large enough for cutting bowl blanks. So, with all of that said, I would guess that for my three saws, I have significantly less invested than I would have in one new saw.
Parts are not really an issue. Ball bearings are pretty much stock items. Babbitt bearings are a bit more complicated in that they are not install and forget. They will last a lifetime (the turbines on the Hoover dam turn on Babbitt bearings), but they need to be oiled with each use. Four of my machines, my jointer, a lathe, a drill press and a planer are Babbitt machines. Band saw blades are consumables, and they are available from in any width or length from many sources. Even now, we have a thread running here that deals with making your own band saw blades from coil stock.
Get the saw that suits your needs. I think that a 20" saw is the best all around compromise in the size department, but others may not agree. Whether buying new or used, be alert for power requirements. Larger saws will likely require 240 v circuits. Some industrial saws will run on either single phase power or 3 phase power. Neither presents insurmountable problems, but know what you are looking at.