For a while there really was a difference in Speer's Gold Dot and Proload's. In the old days, Proload had a hotter load, i.e. higher muzzle velocity, but eventually Speer raised theirs as well, and I don't believe that there is much of a difference now days... You can tell the newer Gold Dot loads from the older ones because the newer Gold Dot bullets have six serrations, while the older ones had eight? (Gee, forgot how many serrations the old ones had for sure.) I believe the change in serrations was to help with deeper penetration.
Proload makes an excellent round, and does not exhibit any more muzzle flash than other premium rounds. It is also a very consistent round, i.e. small deviations in muzzle velocity, which translates to an accurate round... I don't think that you can go wrong with Proload...
Something to think about in terms of price, is that I believe Speer packages the Gold Dot in boxes of 25 (or at least used to), while Proload only has 20 per box...