“Easy” is going to depend on the individual dog and your capabilities. There isn’t a right or wrong answer for which one is easier because you could get a dog that was never trained properly and responds perfectly to your style of training, or a dog that went through thousands of dollars worth of training and the owners gave up leaving him to be someone else’s problem. You could also get a puppy that is eager to please and ready to learn, or you could get a puppy that has confidence issues, hides, and submissively urinates when she sees you.
You are the only one who knows what you are comfortable with. If you meet an older dog, take him for a walk and spend sometime with him, you might find you are totally in sync and decide to adopt! But if you think you’d rather tackle the responsibility of training a puppy “from scratch” then go for it!
Just make sure you research breeds, know your limits and what you can provide.