1.Will it better for me to call for an appointment?

Feel free to call if you cannot use the online appointment function. If it's off hours, do use the online appointment function so that you can get in sooner.

2.How easy is it for me to request an appointment online?

Your appointment request is done in real time. This means that when you request a slot of time for appointment, that slot is booked immediately. However, it doesn't mean that you are guaranteed to be scheduled for that time slot. Wait for a confirmation.