If he likes using a regular cup, let him at it :D Let him experiment in an easy to clean area (maybe in the kitchen) so he can figure out for himself how much he can handle at a time.
My daughter never used a sippy cup or anything like that (no bottles either). When she was a baby she used a cup when I couldn't breastfeed her and dad had to give her her dinner, but by 7 months she wanted to do it herself and was able hold and drink from a cafe au lait bowl and mugs with minimal spillage around her first birthday she had a handle on drinking from sports bottles, but was not able to figure out straws until she was almost 2.
If your son is not coordinated enough to handle a cup, try larger bowls (like small cereal or soup bowls). Also the weight of the container may be difficult to adjust to--I noticed my daughter had A LOT more trouble with light plastic & paper cups. She was fine with regular ceramic or stainless steel cups and even ok with wooden cups, but the plastic ones were way too light and she'd spill them every time ;-/