Curious Cat Question

If you had to buy one book, which would you pick:Victor Pelevin's The Helmet of Horror or...

As his addition to the Myths series, celebrated Russian novelist Pelevin creates a brilliant new telling of the myth: a group of strangers find themselves in a modern-day labyrinth, trapped in identical rooms, given archetypal screen names and able to interact only through a chatroom thread begun by one "Ariadne." The figures who inhabit this doomed maze are drawn from many sources, for instance, "Romeo-y-Cohiba" and "IsoldA" both look for love, but are stymied when they try to find it with each other. All are haunted by the "Helmet of Horror," which is both the machine that controls their destiny and the mind that creates the machine, and there is no Theseus to save them. Pelevin has updated this myth in an absurd and terrifying metaphysical consideration of the labyrinths in which we all find ourselves and the traps we willingly enter as we move through our lives.

...Thomas Pynchon's Against the Day?

It all begins in 1893, with an intrepid crew of young balloonists whose storybook adventures will bookend, interrupt and sometimes even be read by, scores of at least somewhat more realistic characters over the next 30 years. Chief among these figures are Colorado anarchist Webb Traverse and his children: Kit, a Yale- and Göttingen-educated mathematician; Frank, an engineer who joins the Mexican revolution; Reef, a cardsharp turned outlaw bomber who lands in a perversely tender ménage à trois; and daughter Lake, another Pynchon heroine with a weakness for the absolute wrong man. Psychological truth keeps pace with phantasmagorical invention throughout. In a Belgian interlude recalling Pynchon's incomparable Gravity's Rainbow, a refugee from the future conjures a horrific vision of the trench warfare to come: "League on league of filth, corpses by the uncounted thousands." This, scant pages after Kit nearly drowns in mayonnaise at the Regional Mayonnaise Works in West Flanders. Behind it all, linking these tonally divergent subplots and the book's cavalcade of characters, is a shared premonition of the blood-drenched doomsday just about to break above their heads.

I've been meaning to try either writers but I only have GC for one book at A Different Bookstore.

Give your answer and-- more important-- why you chose such and such. Curious cats wanna know.