First, let's keep this thread spoiler free. For my own sake.
I've read the Technomage and the Telepath trilogies, and I found the mage books better than the teep books. The Centauri trlogi is lying ready on the shelf. From the votes thus far, I gather I'm in for a real treat.
Maybe people like the books with the most familiar characters? In that respect, the mage books have the advantage over the teep books, and the Centauri trilogy has the advantage of Vir and Londo as main characters.
Without spoiling anybody, I also find the mage books to have more of a story arc than what the teep books had.
The Centauri books answered what were for many the most urgent questions remaining from the tv series. I find I enjoy the technomage trilogy less with rereads. The contradictions between the books and what we see on screen bother me more now than they used to.
I feel the first Psi Corps book's one of the best at providing background. I love seeing the "setup" of things, with all of Lyta's ancestors and the explanation of Bester's parentage. Kevin Vacit is such an interesting character.
The Centauri Prime Trilogy was probably the best at using the characters we know and love, so I fully understand why people like it. The last book felt slightly rushed, however, and Vir in the Shadow base seemed a little bizarre.
I actually chose Teep, Centauri and Techno-mage (in that order).
I liked Teep book #1 because much of it was so out of the B5 timeline it was very different and interesting. Teep #2 I must admit, I don't recall the details but it was set during B5's timeline. My favorite of the bunch was book #3 because it did after all deliever on "Bester's Fate". It did tweak me how it passed the Telepath War, but we always have that movie to hope for.
Both the Centauri and Techno-mage trilogies dealt too much with previously known information, filling in details without really breaking any new ground. We already knew the outcomes. Also, I often felt these two books were trying too hard to tie threads together and give meaning to everything, especially the way the TM trilogy spends a lot of time revising history at Sheridan's expense.
I was rather surprised actually, after getting around to the teep trilogy, how much I ended up liking it. I'd quite left it last .. thought it wouldn't be too interesting, as the whole Psi-Corps thing wasn't my favourite part of the show, and only got around to ordering and reading it when I'd run out of other things to read.
One reason why I liked it was that it seemed the most "autonomous" of the three trilogies, quite capable of standing on its own as a separate novel trilogy, not just as a tie-in to the show itself. Was also the best written of the bunch in my opinion (but that's a matter of taste).
I liked all three trilogies as such .. Centauri one was the one that interested me the most as far as subject matter goes, while the technomage trilogy was a good & entertaining read but didn't leave me with a lasting impression once I finished it.
Not much of a question in my mind. The Technomage trilogy was the one I enjoyed the most, because the charactors actually "spoke" in the voice of the TV charactors, and so I found it very appealing. Plus, it answered the true, deep questions of the two series that were answered nowhere else. It had a few "clankers" where you realized the author was going against what we saw on the screen, but they weren't vital.
The Centauri series was less well written but still quite good. Vir wasn't particularly believable in some cases, and there was a bit of deus ex machina involved, plus some more serious clankers.
The Psi Corps "trilogy" suffered from the necessary uneven pacing forced by the fact that it wasn't charactor-driven at all. The third book was quite well-done, but neither of the first two seemed to be B5 books in any important ways. You could have removed all the references to the B5 universe without effecting them in any significant way. Not the author's fault, perhaps, but true just the same.