I've used satinwood for radiators. It doesn't smell as much as gloss and IMHO gives a better finish. The big DIY shops will mix satinwood to whatever colour you want so you can match or contrast the walls. Allow it plenty of time to dry (weeks if possible) before turning the heat on.
Emulsion won't stick to the existing finish very well so you could find yourself repainting them in a few months. I have tried special radiator paint but it's rubbish. It dripped and I could get a good finish with it.