I've never used the FD 100/4 Macro, but it is the only Heliar type in the FD line, so how bad could it be?

The Tamron SP 90/2.5 or 2.8 macro is another winner in that range.

My favorite though is a Kodak Medalist 100/3.5 Ektar that I adapted for Canon FD (from a junker Medalist purchased from no less than George Eastman House--I wouldn't cannibalize a working Medalist, of course). Here's a little piece I wrote on the adaptation--