What limited experience I have, is almost exclusively with changa and enhanced leaf. I haven't yet successfully vaporized pure freebase, and I haven't even tried oral administration so far. I did experiment a bit with harmala:spice ratios in changa.
I think enhanced leaf without any harmalas should in theory be almost identical to vaping freebase, if you use a 'psycho-neutral' carrier herb and if you can inhale enough smoke for similar amounts of dmt at once. It may be hard to find such a herb though, as I feel like taste alone can alter the experience too.
For me subjectively, enhanced leaf produces more airy, liquid, translucent, pastelly open-eye visuals. My visuals are less consistent, more variable from session to session. It doesn't have very much effect on my body. I just feel as solo tripping - things are new but familiar, there is just me and the universe.
I haven't gone very high with enhanced leaf dosage though.
With (rue) harmalas, things are different.
My open-eye visuals are more opaque and get more glowing colors - not necessarily bright but deep. I get more of a tribal feel. I usually first see a rotating circular kind of mandala with hieroglyphs that sometimes dance - eyes open or closed.
The most striking difference to me is the benevolent presence accompanying/leading me through the experience. I feel it every time with changa. I also kind of felt it when I vaped only harmalas and smoked weed. I haven't combined harmalas with anything else so far.
The harmalas seem to not only modulate and prolong the spice, they are like a thick liquid that slows things down, like a cloud of mirror particles that reflect the close past/future into the present moment (and analogous for dimensions other than time). They feel like whipped cream to me - probably that makes no sense to anyone else :/
Physically, they make me a bit like drunk - warm, happy, clumsy, difficulty with balance, but without shutting off the brain. Especially at larger doses, the combo flushes my body with energies, which can lead to strange movements that feel wonderful. This sometimes goes so far that I probably look as if I had seizures. I think this is a form of purge, and I've also experienced other forms of purge with changa, most frequently salivating.
Now for the ratios.
The first changa I made was 1:1. This was nice but very strong. I consistently became almost more tired than hallucinating, I had to yawn uncontrollably. The harmalas effects lasted way longer than the dmt's. It was quite pleasant though. If I was to always smoke just one pipe, I might've stayed at 3:4, maybe 2:3, something like that.
With these harmala-heavy ratios, I felt that at the dose that made me happy dmt-wise, I wouldn't want more harmalas, so I couldn't smoke more.
With 1:3, the balance is perfect for me. I haven't tried lower than that. It's enough harmalas to enable all the mentioned effects, but not so much that the body component dominates. The effects of dmt and harmalas fade out at about the same time, and if I want to smoke more, I can do so (sooner for stronger, later for longer, or both).