I liked having my car on Samui. It was a long trip from BKK and if you don't get to the ferry at the right times the waiting can be a drag. Much safer than a motorbike IMO. If you can rent a car while there consider it. I've been to Samui four times and Limbo helped my find a rental on one trip.
I have to agree with funrecdiver, in that having a car in BKK-Pattaya makes things much better. I really enjoyed the ease and relative low expense of diving Pattaya from BKK. Driving can be a headache with traffic in BKK and in general takes a little getting used to, but if you are armed with GPS and patient no worries... I wish I had a car on Phuket because of the rip off taxis. Meter is best!
I have to agree with funrecdiver, in that having a car in BKK-Pattaya makes things much better. I really enjoyed the ease and relative low expense of diving Pattaya from BKK. Driving can be a headache with traffic in BKK and in general takes a little getting used to, but if you are armed with GPS and patient no worries... I wish I had a car on Phuket because of the rip off taxis. Meter is best!