What's the difference between and HMO insurance plan and a PPO plan?

Which is better to have or is there another type of plan thats even better than those? Is there a specific type of company thats better. I have Blue Cross/Blue Shield now but want to switch to Aenta, but there are other options. I don't go to the doctor much, I'm a healthy 25 year old male with no medical problems. Whats the best kind of plan? I can also choose between a CHPA or an HHPA I believe is what they are called.