HELP: choosing between PostgreSQL vs MySQL

Hi greeting,
I am new to Linux.
Appreciate advise and comment on choosing between PosytgreSQL vs. MySQL.
Both to be run under Linux. How does these two database compare with MS SQL
7.0?

There are two options to configure the data base,
a) The data base will have a few million rows, each row is about 100 bytes.
One of the column (field) will be a pathname (filename) to index to an
external files for storing images. Each image belongs to a particular row
and image is 3 to 20 kb (variable size jepg files).

b) same as the about, but the image will be stored as one filed in the data
base. In this case, the data base will be much larger and wonder if it is
size is okay (speed, capacity, etc...)

TIA

Simon