I haven't used either for years, but when I last did, it depended on whether I was using LME or DME. With DME I would add about half at beginning and half in the last fifteen minutes of the boil. LME I would add in the last fifteen minutes.
I preferred a late addition because of darkening, and because I had experienced a metallic taste from boiled extract. It also increases hop utilization.
While I don't do extract additions, I of course add candi sugar and other things to beers. To keep them from going to the bottom I use a long handled quart dipper. I start by immersing the dipper in the wort to warm it up. I then empty the dipper and pour in the sticky stuff. Slowly lower and raise the dipper in the wort until it dissolves and flows out of the dipper.