There are two aspects to consider in respect of tyre durability - one is wear resistance, and the other is resistance to conditions. A low rolling resistance tyre which is designed for economy should provide greater wear resistance than a comparable performance tyre. However, all tyres are susceptible to long-term damage caused by extremes of temperature and UV damage while parked, and given your tyres have experience cracking and have covered only 18,000 miles in three years, it is likely these factors that have caused them to perish. A premium brand tyre may be more resistant to these factors due to a superior compound, but a cheaper tyre will be less expensive to replace if your mileage will continue to be low. You may wish to consider how your vehicle is stored, and look at keeping it in a garage or using a car cover to reduce the impact of heat and light.