Every kid is different when it comes to potty training. My son started training at 2 1/2 years and it took almost 6 months including a new baby sister regression in the middle. He would pee in the potty most of the time, but not poop. I decided I couldn't do the back and forth between diapers and pull-ups. As others have said it seemed self defeating to give them a diaper to depend on.
The three things finally helped. I believe that it takes a village to raise a child and thankfully my parents live in the area. I wanted to avoid bribes, but they really helped. First, Grandma introduced gummy bears as rewards. I'm a bit of a stickler for sugar and artificial colors and stuff, so we switched to trail mix. 1 for peepee, 2 for poopoo, 10 extra for going dry and clean all day.
This helped, but eventually he hit a point where he could go on the potty but sometimes he chose to stay, play, and have an accident instead. We had a man-to-man talk about it, and I started putting the toys that were involved in the accident into time out after the transgression. They only got to come back out the next morning. He would point to them throughout the day and remind me why they were all out of reach.
The final thing was that Grandpa promised to take my son on a real train after he was totally potty trained. We decided that three weeks with no accidents would be the goal. We got a calendar and stickers. Every morning he got to put a sticker on the previous day if there were no accidents the day before. Then he got his 10 extra treats. We explained what three weeks looked like on the calendar and put a little train picture at the goal day. After having to move the goal day back several times, one day he jumped up from playing and yelled, "No more accidents, go on train with Grandpa!" He made it to his goal after that. We've had very few accidents since. Grandpa took him on the TRE from Ft. Worth to Dallas and to the Dallas Zoo. He still talks about that trip to this day.