I have been using aluminum molds almost exclusively for the last 25 years, but am starting to think about a brass mold for better heat retention. I don't know many people who use brass molds, is there any disadvantage to using brass?
I have had good luck with iron molds also but I like the idea of not having to worry about rust. 
thanks!
Joe S

Brass molds turnout the most perfect bullets you've ever seen. The only objection, if it is one, is the weight. A 4 cavity can be a bit heavy compared to an aluminum, but not that much more than an iron one. By all means get one and try it. You'll instantly fall in love with it. 

What make and bullet are you thinking of? Mine are all from MiHec: (You need to Login or Register to view media files and links). They're all perfect and much less expensive than any american made molds. Here is a review: (You need to Login or Register to view media files and links)

I have an Old West brass bullet mold, and it casts nice bullets. Tom at Accurate makes some nice molds.

i have brass and like them too, also have 35 or so iron molds, rust has never been a worry or concern. care for them and they will out last you. i spray mine with wd-40 and put them back in the box when through with a run of bullets. 45 yrs and no issues!

I have some 60 moulds.  The very best one to use is brass, made by Norman Brockway back in the 1870s.

I for one, am glad to see this topic come up for discussion. I am heading towards the purchase of a new mold and I have both aluminum and steel/iron molds. I was thinking about a brass mold and from what I have seen here so far, it would be a good choice.
Sam

I thought I had answered Jeff's question as to what mold I intended to order from Accurate Molds. Not sure yet but probably a 315J or 300J. He made those at my suggestion, I have the aluminum version, but due to zinc contamination and other reasons, some of which I have not figured out, I am NOT getting good bullets. A new mold is a lot cheaper than spinning my wheels. 
Joe S

Joe S,
A new mold alum,brass or iron will not solve your problem of poor casting
if you do indeed have zinc contamination in your alloy.
I suggest you go to a new batch of alloy and perhaps your existing mold will cast good bullets again.
Been there done that. I very carefully sort my WW to be sure of NO Zn ones. Easy to do with a utility knife. lead ww cut smooth, Zn ones, the blade chatters if you try to "shave off"
on it. Tedious sorting, like I did last night to another "lot" of WW, but better than losing a 60 batch to Zn contam.
beltfed/arnie