Hi, my 2 cents worth.
I always upgrade to a new version of Mint by the manual partition method.
I always reformat my root "/" partition and install the new Mint clean.
I always have a "/home" partition that I don't format.
My configuration is 20GB for root (/) and formated, then 1GB for the swap, then remainder for /home and NOT formatted.
I also use primary partitions for all of them, but have no good reason for doing that
I place swap between system and data so that if it starts to use swap the heads aren't flying from system partition to the end of the drive back and forth.
(placing swap after root is probably just a personal thing with me and not really an issue)
I would suggest using 1GB swap for any size RAM.
The rule of thumb is the less RAM you have the more chance u will use swap and the bigger swap you should have.
In practice, if you ever got to 500MB of swapped memory you would be rebooting your PC because it would be running so slooow.
Even on my 8GB RAM system i get some swapping out to /swap partition over time.
So whether you have 2GB or 16GB ram, just go with 1GB swap partition.
My /home partition is always left alone with my data on it but I don't let Mint install into my /home/myname directory.
Before I start the install I browse to the old /home partition and rename /myname to /mynamezzz
Then I can install Mint clean to the /home partition with my same username (myname) and have all clean and known to working configs.
After install I can move all my "Data" files over from /home/mynamezzz/ to /home/myname. This is instantaneous because they are on the same partition.
If I then want to transfer over some config files I can play around with that, but I tend to just rebuild my configurations from scratch believing it will be more stable that way. After a month or so and I'm sure I have all my data and things are working fine I delete /home/mynamezzz directoy.
That's it - a completely clean install of Mint with stable default configs without losing your data files.