After loads of research and trawling the internet for info I finally opted for a warm air system. I suffer badly from hey fever and the air filtration cleaning offered by the newer warm air units has been a godsend for me. I opted for the Cleanair filter. It's been great. Apparently these filters remove up to 95% of airborne molecules. Some of the other stated benefits of newer warm air systems are efficiency, quietness and constant temperature. I'm not sure about those things because I've found warm air to be a bit noisier and slightly more expensive than central heating.
However, for pet owners and allergy sufferers the air filtration of warm air heating is a huge bonus.