Phuket Rent a Car

Rent a car in Phuket is possibly the best option for travel around but with strings attached.

The first problem is there are no drop off rentals, means you always must bring the car somehow back, the same is if you use a motorbike.

E.g. You could rent a car using Pure Car Rent and drive with it wherever you want, when crossing the border (only to Malaysia) a full insurance must be made. Do it on the Thai side for about Baht 1500,- for a few days. It also needs to already have the car paper translated from Thai into English which takes about 3 days. 

Pure Car Rental

If they catch you in Malaysia without a local insurance it costs Malaysian Ringit 300,- fine, you run into deep trouble when having an accident and no insurance. The insurance offices at the border are only open from about 8 am to about 6 pm. Use a insurance office before the border on the Thai side, there are small booths on the road side. Don't do it on the other side, the people in the offices there are very lazy and unwilling to work at all.

People in both countries can get their driver license 

without any serious education, means a real helter skelter on the roads. If an accident happens they will always blame the foreigner to be responsible. It wont matter what actually happen even if it absolute and 100%  clear that you might not be responsible. They will bend and twist and come up with some strange excuses to make you responsible.