Putty is just a ssh client. Terminal is a shell that has access to ssh so you can access your own files or redirect ports easily through a remote ssh session(you can do this with putty but you must go through some hoops, ie. loopback device and setting up some ports in the putty config), etc.... I love the tabbed terminals that terminal provides. I can ssh into a work computer and have my local shell in another tab. Very seamless.