I have done both. Ayahuasca when I was 17, and smoked when I was about 19. If you are planning on doing either, go for an ayahuasca preparation.
I had a friend who came back from South America with a bit of psychotria viridilis, which contains DMT. He got it from one of the locals. I have no idea where you will find this in the US, or if it is even possible, so unless you go for a smuggling run, you might be screwed. There are, however, many other plants that naturally contain DMT. The most notable of these is peyote, which is widely believed to only contain mescaline as an active chemical. If you really look around, you might be able to find something. The natural MAOI that we used was peganum harmala, which we ordered off the internet. There are plenty of recipes online, so you can switch either ingredient with another suitable one that you can find. Drinking the tea will bring you a very strong trip, but nothing that will shake an experienced entheogen user (not just someone who has done LSD or mushrooms a couple times). Then again, we might just not have made a very strong tea, as we were working with limited resources. All in all, it was a good, but uneventful trip.
Smoked DMT is a different story. I happened upon a little bit of DMT freebase a couple years later. A guy from whom I often bought research chemicals had a little personal stash. I had to pretty much interview for it and beg him to sell me some. He finally caved in, and sold me what he said was about 2 decent doses. I shrugged off about 50 warnings from the guy, and went to smoke it with my best friend. I went first. I took one big hit off the pipe, and that was all I could do. It was probably about 5 seconds before everything just kind of melted away, and I was sort of left in this empty world. The visual hallucination was very strange. It was sort of like pictures in my mind (thoughts) were distorting things in the world, and I had an intense "floating away" feeling. I didn't see anything that wasn't there, it just seemed like nothing was the way it was supposed to be, and I didn't belong. I also remember having a bit of trouble distinguishing between which was which (thoughts and surroundings). It's incredibly hard to explain. The aural (sound) hallucinations were terrifying; with roars and moans mixed with something like the inside of a washing machine. The bulk of the trip was very hazy. I came down muttering incoherently about life and death, and how they are the same thing or something pschadelically "quasi-poignant" like that. I also should note that I started on a chair, and ended on the floor a few feet away. My friend was babysitting, but said that it seemed to be better to just let me go than try to restrain me. The trip lasted about 15 minutes. It felt like a lifetime. I had to convince my friend that I was alrght before he decided to go. He said that watching me was scaring the shit out of him, and that he was trying to talk to me the whole time. I don't even really recall him being there. He went afterwards, and wasn't violent or anything, but certainly wasn't responsive to anything. He described his trip as being much more visual and playful. He even stayed in the chair.
I am sorry if this was confusing, but I am trying to recall this from a little over 5 years ago. The point is, that shit kicked my ass. I don't regret doing it (smoking), but I will never do it again. If I have the opportunity, I would like to try Ayahuasca again. I don't think our tea was as potent as it could have ben. I have never even heard of it since we did it. I think we probably got the recipe off of Lycaeum.org.
Bottom line: Neither preparation is to be underestmated. I wouldn't recommend doing either unless you are very experienced. By the time I smoked DMT, I had at least 100 trips under my belt, using various tryptamines and phenthylamines. It was much much more intense than LSD or mescaline, or anything else I have ever done, and I am (and was) quite prolific in entheogen use.
But, if you have the means, and you are prepared to have respect for the drug, then go for it. But be careful.
S-town
P.S. I'm sorry if this is a little ranty and verbose. I'm pretty baked.