What to look for when renting/buying new car

Road tax: this is mostly proportional with the engine size and car efficiency

Insurance cost: in my case I had a new licence with no discounts, I picked up some cars that I liked, then when I tried to get quote for insurance, the value was very high. I did several trials with several cars, found out that the value goes down if the car is newer, and the value goes down with the lower engine sizes. So in my case to get a car with acceptable car insurance value, I was looking for cars > 2007 and engine size < 1.6

Low running costs: lower miles per gallon are going to save on the long term.

Known problems: search for the car model problems: this is very useful to find if this model has any problems, an example for this, when I was looking, I liked the Citroen C4 Grand Picasso automatic, when I searched for its problems, I found out that the automatic version has short life clutch problem, and that transmission is not very smooth, so I didn't go for it.

Warranty: if available that will be better.

Any coming costs: Do you need to replace the tires, battery? Change the oil? Pay tax? Pay yearly inspection? Think about any expenses that you will pay during the first year. 

Resell price: once day you are going to sell it, so better not to lose much when selling it.