Can you be more specific? A lot of ordamental breeds are not known to be the best layers but can be great eye candy. While you may sell them well at first the local market can be satisfied sometimes quickly. It depends on the area. Those birds also tend to be a bit flighty from people I have talked to. Seabrights, D'uccles, Silkies, and Polish are all popular tho I have not raised them. I am getting silkies as brooder hens. I am looking at mottled cochin bantams for brooders and to possibly sell but I am not sure yet. They are not as exotic as seabrights but not as flighty so they might be better for me.
In my opinion from what I have seen the breeds that sell are the dual purpose breeds. People allways need to replace ageing layers. Rocks, RIR, Sexlinks, Austrolorps, and Orpingtons, allways sell.
If you want rare, then get into somthithing that almost no one has. Jubilee orpingtons are newly re-imported into the US and have gotten a bit of attention. I just can't justify the cost of good chicks.
The way my mind works is if you plan to try to make a little extra money without putting tons of upkeep work into it then have what people need. Not what people want. They need food. They want a exotic show bird.
I could be totally wrong on this is just my own opinion. I would try to get to a show and talk to some breeders in your local area. And hopefully others will get on here and give you other opinions so you get a chance to see things from othe sides and make a choice that is best for your situation.
And don't rush into it. Take your time and research. Hope this helps.