Whats the best anti rust primer ?

[rac]

have used a zinc rich primer called GALVAFROID on some wrought iron gates with great success a few years ago and they still look good.not cheap but can be over painted and i'm sure would be ideal for underbody protection.used extensively in industry so must be good stuff.Anyone here used it?
rob.

[stag888]

Thanks to all for your input , am not sure if I'm not now just more confused , however shall use the next week to try out a few combinations on some scrap , and see what feels the best - just need to keep reminding myself - whatever goes on will be 100 times better than what was there before - nothing basically . Cheers Steve