Both options can cause some pain, but most people believe that once healing occurs, dental implants are less painful.
Dental implants require invasive surgery and an extensive healing process, which can result in some minor discomfort. However, this is about the same as you would experience with tooth extraction. Once you heal, you should have no more discomfort.
Dentures sit on the gums, which can cause pressure and/or friction sores. This typically resolves after some time but may continue if they are not properly fitted.