Hi Lauri,
You could say the sun is medium sized. This is because there are plenty of stars both larger and smaller than the sun. However, actually there are more stars smaller than the sun than there are larger. This is because there are many more small stars than large ones. Smaller stars are much longer lived than larger ones.
There are pictures and information about the Pistol Star here:
http://antwrp.gsfc.nasa.gov/apod/ap971008.htmlhttp://www.solstation.com/x-objects/pistol.htmIt is thought to be 100 times more massive than the sun and is in the constellation Sagittarius, the archer.
Whether that makes it the biggest star depends on how you define "big". Is it mass (how "heavy" it is)? Volume?
Last year astronomers reported finding the largest stars in volume,
KW Sagitarii (9,800 light-years away), V354 Cephei (9,000 light-years away), and KY Cygni (5,200 light-years away). These all have radii about 1500 times that of the sun (see
http://news.bbc.co.uk/1/hi/sci/tech/4164365.stm)
You can tell from their names that these stars are in the constellations Sagittarius, Cephius (the whale), and Cygnus (the swan).
These stars are relatively low density (fluffy), though, so they are not as massive as the pistol star.
Terry