How does a committee select received manuscripts for poster presentation? What are the differences between papers that are chosen for presentation vs those which are accepted for poster presentation? Is one less reputable than the other one? How does a committee select received manuscripts for these two categories?
It might be useful to look at it from the conference organizers' perspective:


Accepted full papers usually require the author to give an oral presentation at the conference. But the number of time slots for those presentations is usually limited by the size of the venue (number of conference rooms), and extending it either costs the organizers additional money or is not possible at all. So there is a strong motivation to limit the number of accepted full papers, and to choose only those that represent the largest impact/progress to the research field.
Accepted posters on the other hand are usually presented at a short (~1-2h) poster session, where many posters are presented at the same time in a rather small area. Each conference room booked for the oral presentations can probably be used to present 50-100 posters in a single session, and scheduling a second poster session can cheaply double that. So there is no real motivation to limit the number of accepted posters, beyond making sure that they make sense and represent at least a minor step forward.


These perspectives also match my experience on acceptance and gained reputation in the field of computer science: You can get pretty much anything accepted as a conference poster, while getting a paper accepted is much harder. For that reason, accepted posters are largely irrelevant scientifically, and - in my experience - are usually not even actually published in the conference proceedings (sometimes the proceedings at least contain the extended abstract that was submitted for poster acceptance, sometimes not even that).