Ayahuasca obviously takes longer to come on, which a lot of people like. It tends to come with nausea so a purge is often involved. It can be a very powerful experience, and really gives you some time for some deep exploration. The harmalas in the ayahuasca, change the very character of the visuals/visions. To me, everything is expanded a bit. It's almost as if there is an extra "order" superimposed on the visions. Every time I take ayahuasca though, I'll end up smoking DMT with it to get the best of both worlds.
In my own preference, smoked DMT is often more up my alley. I personally am not that great with waiting for the ayahuasca to come on. Whereas many prefer the smooth transition into the space that ayahuasca offers, I'd much rather just be instantly plunked right into the heart of it. The major drawback of course is duration. If only the pure DMT experience could be made to last for so long. There's something about the purity and conciseness of the visuals from pure DMT without any harmalas that I've grown to prefer. On the other hand, I've had some of my greatest experiences with aya/pharma, so I have a respect for it as well. It's the sort of thing that I prefer to keep more occasional. I like having my aya experiences spread out over a long course of time, so I can't mentally adapt to them as easily as smoked DMT. I like for it to feel like a special occasion. That and I can't deal with puking on such a regular basis. I ended up losing a lot of weight when I started taking ayahuasca.