I've never changed money in TST. It's more a matter of bad reputation than anything else.
I'd say prejudice more than reputation. The rip offs happen in the camera shops.
You can head up to Mongkok or over to Causeway Bay or just about any major shopping area: there are plenty of small exchange places around. Most cater to Mainland visitors and post RMB/HKD rates in the window, but they also do USD/HKD. Rates are almost always posted on the back wall, so it's not hard to eyeball two or three shops and get a feel for the right rate. As I said, there are a small number of shops known for rip-off rates -- usually the spiffiest-looking ones -- so check the posted rates very carefully.
Banks will charge fees and are not worth the hassle.
Why go so far when TST has places with the best rates.
Try Chungking Mansions, 1/F, Pacific exchange. Do not change outside banking hours for the best rates. Also in Mirador Mansions on G/F are a few changers with good rates.
Exception: Best rates for RMB exchanges are on and around Cleverly Street in Sheung Wan near the Macau Ferry terminal.
For an idea what the spreads should look like on that day, check here
http://bcel1985.blogspot.de/