It's hard to separate the experience of looking at individual artists from the fair sometimes. After going to more than one fair though, there are trends that come forward that are built-in to the individual fairs. ABMB is the big fish and demands a certain level of respect, but everyone I know has thought, at one point at least, that going to Basel is less rewarding that a certain other fair that they loved. What makes Basel not PULSE? What makes PULSE not Aqua? etc. Each fair has a personality behind it that directs the fair. I'm not concerned with the people who run them here and their personalities, but they have reasons that they include or exclude galleries and those verdicts have consequences for the feel and the qualities that the fair has.
PULSE is one of the fairs I've always felt comfortable visiting. The galleries that participate are for the most part, very serious spaces that try to show their best work; they attempt to keep up the dialog but are presented in a space that increases the individual object's objectness. There is something about the place PULSE is in that you can see how these things can come home with you and be in your life. With Basel, those objects feel just as discrete and salable, but they tend to be blown out by the shear size of the convention center and you are unable to see exactly how large they are or aren't. I'm not sure my tiny apartment could fit most art I've seen here, but that information is hidden because walking around Basel is like living in the ideal white frictionless cube in which physics experiments happen.
UNTITLED's tent on the beach also makes it hard to have any idea how big things are, but a lot of the work at that fair are not made to be discrete objects. Many of the "works" are not really simple things that have an edge but are installations; congregations of things that build up into an arranged whole. These formal systems don't all function the same way; some are conceptual, some deny their formality by hiding their meanings, and some (in truth) could be confused for decorations. But it is undeniable that UNTITLED is filled with vivid art that is not as quick to read. There are very few one-liners there. One of the more subtle things at UNTITLED is that it is the fair with the least amount of flesh (images of people or bodies) or narratives on display. One can find various meanings (including seeing something that probably wasn't intended by the artist) but you need to spend some time and not just rush by the work.
Both positively and negatively, PULSE and Basel have a much wider range of working conditions—from photographers who capture snapshots to tech art to figurative sculptors to "edgy" sculptures of a pig made from prayer rugs—these shows are edited by their gallery's means and not as strictly for their content. The difference between those two fairs is huge and unmistakable, but it takes a bit of effort to be able to explain what that exact difference is. It's useless to consider if one is better as you'd have to answer the question, better for what? Seeing Ai Wei Wei or Takashi Murakami at PULSE seems out of place, even if there are galleries at PULSE which do deal in his work. You can see tons of artists at more than one fair, or even booths at the same fair, so it's not a problem per se, but it's a matter of audience expectations.
Simply, the artists and galleries at Basel present themselves as ready for big museum shows. Their work is developed enough and distinguishable from their colleagues to be considered dependable for even the most cautious curators. PULSE is filled with fantastic artists and galleries, but their work is still classified as emerging (again, for the most part; this is not a strict rule, but a reflection on the vibe you get from these fairs). There are tons of artists at PULSE who I'd be happy to see in monographic shows at museums, but not all of them will get that call soon. For every Gerhard Richter at Basel, there is someone like Hendrick Kerstens, Manfred Mohr, Allison Schulnik, Scott Hunt, Grant Miller, Gregory Euclide, Laura Ball, Rachel Perry Welty, or Mary Waters; all of whom are on the scale of emerging artists, have shown in great museums, and none of whom are next up for a solo at the definitive Museums.
Aqua? It's a great fair filled with smaller and inexperienced galleries. Are there fantastic artists and galleries there? Yes, and the work you see there runs a huge range from student work (The Georgia State University show made some of the galleries look like amateurs), to work that might fit happily into various other fairs. Things like the Miami Project leave me a little less sure on how to describe it. Their individual galleries have an even wider range of quality, experience, and artists but have even less of a singular style to unite them.
Separating these fairs by their ambiance or their audience is really pointless though, as everyone who doesn't fit these ideas are, of course, now deeply offended by something I just said and we've strayed into very meta-art territory. The art and galleries at art fairs unfortunately do not lend themselves to close reading of the art. First, because everyone gets bogged down in the price tags, parties, and excitement of what might be around the corner, but there is an additional structural problem with visiting art fairs. If a monographic exhibition is like a well thought out clear photograph of an artist and their career, the art fair is like looking at a a film strip: you know that the every frame is slightly different, but after a while, you get so fatigued of looking that you stop noticing the differences. You can't define the fair by the art, nor can you define the art by the fair. If you ran the metaphoric film strip through a projector, that film strip would move and you'd sit still, but the way that art fairs are laid out, you move and the film strip stays still. You have to be careful to pay attention or attributes that you care about disappear and you end up walking right past a display that contains what you spent all day looking for.