Planning my first trip to malaysia. What is the best way to get from george town to cameron highlands?

Taxi.

any thoughts on renting a car?

I rarely rent cars, never in Asia. I much prefer letting someone else do the work while I enjoy the ride.

I arranged for a taxi to take me from GT to CH & pick me up to return a week or so later. I stayed outside Tanah Rata, got around on foot while there, great area to walk, took taxis farther afield to visit tea gardens. For me it was an ideal way to do it.

I regularly rent cars in Asia and Malaysia is one of the easier countries in which to drive. However, the traffic en route to Tanah Rata the main town in the Cameron can be horrendous, especially at weekends. When you get there parking your own car could be problematic which is why most seem to opt for jeep tours to the various sites - way easier. I think a car would be more of a hindrance than a help.

It is a long way by bus (5 hours) from Georgetown so, if you have the time, I think I would plan on a couple of nights in Ipoh, a great destination in its own right and on the way and a nice jump off point for the highlands, great food, a graffiti trail and some stunning cave temples. There are a few posts on our blog re that area of the country @ https://accidentalnomads.com/category/malaysia/

Getting to Ipoh is easy by bus or even better by train , around three hours as I recall.

The cheapest option is to ride a Bus via the terminal Sungai Nibong, but I recommend getting a taxi for a convenient trip (payment range from $125 to $160). Not sure if it's much cheaper or higher now.