There is one major CON that nobody has mentioned yet:
If you jailbreak your phone, you will grow very accustomed to certain tweaks and modifications that you will have a very hard time going without (e.g., for me, I would hate it if I didn't have f.lux, SwipeSelection, Push for Gmail, and many others).
Eventually, Apple will patch some exploit, and it will not be possible to restore to a jail-breakable firmware version. When this happens, you will either have to avoid restoring in order to maintain your jailbreak, or even worse, will be forced to restore and will lose your jailbreak. Once that happens, you will have to wait and hope for a new jailbreak to be released soon.
A jailbroken iOS is always preferable to stock iOS, but I don't imagine Apple losing their attitude of "we know what you want even more than you do" any time soon, so jailbreaking will always have this frustration.