Hi, I know others have already said it, but...big potty, and here's why.
1. Less mess. (Who wants to clean poop out of a plastic receptacle? Eeeew!)On the big potty he can flush it himself without it sitting there until you clean it up. I have read that when potty training on the little potty chair, the child should be expected to dump the receptacle by himself, but I think that is unrealistic. At that age, how can they not spill?
2. Less play. He might see little potty chair as more of a toy and view the process as fun and games, rather than getting down to business. We had a potty that played music, and to my sun it was a plaything, and he just wanted to keep pressing the music button and play around.
3. Easier to go in public because he is already comfortable with the big potty. Once they are trained, it is important not to fall back on diapers/pull-ups, so you want him to be comfortable with a public toilet.
We had a potty chair and he went pee-pee in it a few times, but when it came down to the real training, we went right to the big potty. (seriously, I cannot imagine having to clean poop out of that thing on a daily basis.)Make sure you have a step stool so he can get up on the potty himself. You many want to try the seat inserts that other moms have recommended, but I did without that too, so I would never have to worry about bringing it with me anywhere.