Generation X #1-#25. A great introduction to a great team, as well as most of Hollow's (here called Penance) best stories. If you only buy 25 Generation X issues, make them these Generation X issues. Highlights include:
--Issues #2-#4 - in which the team splits into smaller groups to confront a dangerous, mysterious mutant known only Penance. Penance's goal? Survival, at any cost.
--Issues #12-#14 - Penance's former captor makes a bid to reunite with her (and destroy Generation X), only to be shocked to find that she doesn't want to come back with him. Is there more to their past than Penance lets on?
--Issue #25 - this Anniversary Special finds the team in dire straits, captured and broken. Black Tom Cassidy has thought of everything... everything except Penance.
Generation X Annual '95. A significant issue for Penance as well as nice moments for other Generation X members.
Generation X #57-#58. After the events of #57, in which Emplate makes another bid to recapture Penance, Penance is finally her own person again in #58. But who is this new Penance? Is she dangerous? The team hunt down a fleeing Penance in the woods, only to make a startling discovery. Jay Faerber wrote the story, as the last writer to tackle Penance in a significant way.
Generation X #60-#61. Jay Faerber continues an admirable effort to repair the character following another writer's disastrous origin issue. In what was Faerber's last two issues, Penance carves an ice sculpture, there's speculation about her family, then she takes on the Juggernaut.
The Loners #2-#6. Penance's first post-Generation X appearance and the one in which she is dubbed Hollow. Some fine moments for Hollow in the earlier issues, but the story quickly falls apart in the final two issues. Worth getting if you want a "this is what happened to Penance after Generation X" story with some nice art by Karl Moline.
Generation X Annual '97 and 1999. The 1997 issue doesn't have a great story, but there's a very nice moment for Penance in it, in which she receives a hug from Husk. The 1999 story doesn't focus on Penance, but offers some brief insight into the character within the backdrop of a Jubilee story; heavily recommended for Jubilee fans.
Generation X #26-#39, #41-#53 (scattered issues), #68-#69.
--Some good moments for Penance in the pre-#40 issues, though these aren't necessarily the best Generation X stories in the world.
--Not much to love or hate in the post-#40 (to #53) issues.
--Absolutely nothing of consequence happens to Penance in #68-#69, except a few brief appearances and the explanation for why she's not in most issues from #62 onward; not worth getting unless you're a completionist.
Generation X #40. This is the infamous issue in which Penance's origin is revealed, one that has been almost universally rejected by the fans and subsequent creators.
Avengers Academy #21, #30-#31. Hollow's first post-Loners appearance. Hollow is a background character and remains that way for the extent of her tenure at Avengers Academy.