Many of the large paint manufacturers such as Dulux Trade and Crown Paints produce both water-based and solvent-based paints that are suitable for use on radiators. Modern formulations are as good as each other.
The main differences are usually to do with ease of application, odour of the product and the desired finish. Some paints are formulated to require several coats whilst others just need one. All the different formulations however have been tested to ensure that they give a long lasting, durable finish to radiators.