Dental implant pros: They hold better, more assurance, less to bother with
Dental implant cons: They're more risky (you're drilling a hole into your jaw bone to implant it here), if they don't take then they cost A LOT MORE to correct, they also don't look as natural as your real teeth. Also it can take up to 2 years to complete an implant (there are many different "steps" and healing periods you have to go through first.)
Dentures pros: Cost less, safer for your overall health, less risky, looks more natural to other people, quicker to get
Dentures cons: More to bother with (you have to clean them daily, etc), can slowly erode your other teeth that the anchors are placed on.