What is the best infrared heater to buy?

It depends on a few factors, size of your room, your budget and safety, in case you have small children or pets.

If you've a small room to heat, and on a budget, then the Optimus H-5210 is the best choice, you can still find it for under $30.

If you have a larger room, and want something a bit safer around pets and children, then the Dr Heater Quartz is still the most popular heater for under $200.

You can find reviews for the most popular brands here in the related link.