There are some pros and cons here. Broadband offers much, much quicker speeds for transmitting information.
However, dial-up is universally available whereas access to broadband is still patchy but growing daily.
Dial-Up may still be a cheaper option if you only need to be online for a short time every day, say for domestic email use only.
For constant online access during, say, working hours of 8am-6pm Monday to Saturday, broadband is likely to be cheaper, especially if access time is unmetered.
Broadband is better for connecting a network to the Internet.
You will need to weigh the issues and make up your own mind.