There are three main harmalas.
Harmine,
Harmaline, and
Tetrahydroharmine (or THH)All of the harmalas alkaloids mentioned above can be in pure form (i.e. crystals/powder), both in freebase form or in some salt form, or they can also be dissolved in some liquid/tincture. This depends on what you do yourself with them when extracting (or on what form your vendor is selling them in).
With Harmine, oral dosage for full MAO inhibition is around 200mg. More or less same with THH. Harmaline is twice as strong, so one needs only around 100mg of it.
Harmaline is a bit more sedating/dreamy than the other ones, but I also like it (some people dont). THH seems to be the clearest one by itself but I havent experimented with it pure, only mixed with other harmalas so I cant say for myself. Harmine is interesting, and is usually my choice for pharma because I can easily extract it from syrian rue.
Syrian Rue contains basically Harmine and Harmaline, in
different ratios, plus a couple of other non-harmala alkaloids, Vasicine and Vasicinone. People ingesting rue usually make a tea out of 3,5g syrian rue. I dont recommend it because it tastes bad, usually makes one nauseous, and because vasicine and vasicinone are potentially more toxic. They are uterotonic, so potentially more troublesome for women, specially very dangerous for pregnant woman because vascine and vasicinone are abortifacient.
The harmalas (harmine and harmaline) can be extracted from syrian rue and separated from vasicine/cinone quite easily. Check the
harmala extraction and separation guide for more info, and it also explains how to separate harmine from harmaline if you want.
Caapi vine contains a mixture of mostly harmine and THH, with small to negligible amounts of harmaline.
Caapi Copy is the pure harmala alkaloids from caapi, either extracted from caapi directly or extracted from other sources but mixed in the same proportion of THH/Harmine as found naturally in caapi
Caapi leaves have mostly harmine as you can read
here. Caapi leaves are usually used for making changa, not so much for oral ingestion in ayahuasca.
I cant suggest anything in particular because they are all interesting, you have to try by yourself and see.. Good luck!