I'd read "Q Squared" and "Vendetta".
"Vendetta" was a rip roaring read back in the day. Wish that had been made into a TV 2-part episode before "I, Borg" had. Peter had some fantastic continuation of ideas and set-pieces that really needed to be put on screen. Especially Picard trying to save Delcara. Even the connection to TOS was pretty cool, though there's still a ton of continuity bridging he's trying to write in and at the time it was all fantastic. I sold my copy but, years later, bought another first edition after scouring for a while. Might read it again one day to see how it holds up.
"Q Squared" didn't do it for me as much, from what I recall it didn't have the same natural flow. The integration connecting TNG and TOS also felt forced. It's not a bad novel, but it definitely felt like something was missing, but I'd read that long after the creme of the creme "Vendetta".
Didn't he write a Borg novel involving Janeway?